Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer for each of the questions

Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds – any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants. 

The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them.

In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world’s weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms. 

The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.

The word ‘applications’ in bold could best be replaced by which of the following?

A. treatments  

B. requests  

C. special purposes  

D. qualifications

Nguyên nhân của sự suy giảm tầng ozon chủ yếu là do:

A. khí CO₂

B. mưa axit

C. clo và các hợp chất của clo

D. quá trình sản xuất gang thép

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.

Environmental pollution is one of the impacts of human activities on the Earth. Pollution occurs when pollutants contaminate the natural surroundings; which brings about changes that affect our normal lifestyles adversely. Pollution disturbs our ecosystem and the balance in the environment. Pollution occurs in different forms; air, water, soil, radioactive, noise, heat/ thermal and light Let us discuss the causes and effects of air pollution on mankind and the environment as a whole.

Air pollution is the most prominent and dangerous form of pollution. It occurs due to many reasons. Excessive burning of fuel which is a necessity of our daily lives for cooking, driving and other industrial activities; releases a huge amount of chemical substances in the air every day; these pollute the air. Smoke from chimneys, factories, vehicles or burning of wood basically occurs due to coal burning; this releases sulphur dioxide into the air making it toxic.

The effects of air pollution are evident too. The increase in the amount of CO2 in the atmosphere leads to smog which can restrict sunlight from reaching the earth. Thus, preventing plants in the process of photosynthesis. Gases like sulfur dioxide (SO2) and nitrogen oxide (NO) can cause acid rain.

The decrease in quality of air leads to several respiratory problems including asthma or lung cancer. Chest pain, congestion, throat inflammation, cardiovascular disease, respiratory disease are some of diseases that can be caused by air pollution.

The emission of greenhouse gases particularly CO2 is leading to global warming. Every other day new industries are being set up, new vehicles come on roads and trees are cut to make way for new homes. All of them, in direct or indirect way lead to increase in CO2 in the environment. The increase in CO2 leads to melting of polar ice caps which increases the sea level and pose danger for the people living near coastal areas.

Ozone layer is the thin shield high up in the sky that stops ultra violet rays from reaching the earth. As a result of human activities, chemicals, such as chlorofluorocarbons (CFCs), were released into the atmosphere which contributed to the depletion of ozone layer.

Question 36: What does the passage mainly discuss?

A. How pollutants contaminate the natural surroundings.

B. The causes and effects of air pollution.

C. Our ecosystem and the balance in the environment.

D. Some solutions to air pollution.

c)

Ta có \(a< b< c< d< m< n\)

\(\Rightarrow\left\{{}\begin{matrix}a< b\\c< d\\m< n\end{matrix}\right.\)

\(\Rightarrow a+c+m\le b+d+n\)

\(\dfrac{a+c+m}{a+b+c+d+m+n}< \dfrac{1}{2}\)

\(\Leftrightarrow2a+2c+2m< a+b+c+d+m+n\)

\(\Leftrightarrow a+c+m< b+d+n\) ( thỏa mãn đề bài )

\(\Rightarrow\) đpcm

áp dụng bất đẳng thức Cauchy - Schwarz dạng phân thức

\(\Rightarrow VT=\dfrac{a^4}{ab}+\dfrac{b^4}{bc}+\dfrac{c^4}{ca}\ge\dfrac{\left(a^2+b^2+c^2\right)^2}{ab+bc+ca}\)

Cần chứng minh rằng \(\dfrac{\left(a^2+b^2+c^2\right)^2}{ab+bc+ca}\ge a^2+b^2+c^2\)

\(\Leftrightarrow a^2+b^2+c^2\ge ab+bc+ca\)

áp dụng bđt Cauchy - Schwarz

\(\Rightarrow\left\{{}\begin{matrix}a^2+b^2\ge2ab\\b^2+c^2\ge2bc\\c^2+a^2\ge2ca\end{matrix}\right.\)

\(\Rightarrow2\left(a^2+b^2+c^2\right)\ge2\left(ab+bc+ca\right)\)

\(\Rightarrow a^2+b^2+c^2\ge ab+bc+ca\) ( đpcm )

Vậy \(\dfrac{a^3}{b}+\dfrac{b^3}{c}+\dfrac{c^3}{a}\ge a^2+b^2+c^2\)( đpcm )

Để tạo độ xốp cho một số loại bánh, có thể dùng muối nào sau đây làm bột nở?

A. (NH₄)₂SO₄.

B. NH₄HCO₃.

C. CaCO₃.

D. NH₄NO₂.

Nguyên tố Y là phi kim thuộc chu kì 3, có công thức oxit cao nhất là YO₃. Nguyên tố Y tạo với kim loại M hợp chất có công thức MY, trong đó M chiếm 63,64% khối lượng. Kim loại M là

A. Zn

B. Cu

C. Mg

D. Fe

Cho hỗn hợp gồm Na, K, Ba vào 200 ml dung dịch CuCl₂ 0,6M. Sau khi kết thúc các phản ứng, thu được 2,24 lít khí H₂ (đktc) và m gam kết tủa. Giá trị m là

A. 4,90 gam.        

B. 19,60 gam

C. 9,80 gam.

D. 11,76 gam.

Khi nói về độ pH của máu ở người bình thường, phát biểu nào sau đây đúng?

A. Độ pH trung bình dao động trong khoảng 5,0 - 6,0. 

B. Hoạt động của thận có vai trò trong điều hòa độ pH

C. Khi cơ thể vận động mạnh luôn làm tăng độ pH

D. Giảm nồng độ CO₂ trong máu sẽ làm giảm độ pH

Các bạch cầu đã tạo nên những hàng rào phòng thủ nào để bảo vệ cơ thể ?