Mắt xích chung nhất cho lưới thức trên là:

A. Cây xanh và thỏ

B. Cây xanh và vi khuẩn

C. Gà, cáo và rắn

D. Chuột, thỏ và gà

Cho một vật đang chuyển động đều với vận tốc 2m/s thì đi vào vùng cát. Vật chuyển động châm dần và dừng lại sau khi đi được quãng đường 0,5m. Xác định hệ số ma sát giữa vật và cát

A. 2,5

B. 0,2

C. 0,4

D. −0,4

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

What is meant by the term economic resources? In general, these are all the natural, man–made, and human resources that go into the production of goods and services. This obviously covers a lot of ground: factories and farms, tools and machines, transportation and communication facilities, all types of natural resources, and labor. Economic resources can be broken down into two general categories: proper resources– land and capital– and human resources– labor and entrepreneurial skills.

What do economists mean by land? Much more than the non–economist. Land refers to all natural resources that are usable in the production process: arable land, forests, mineral and oil deposits, and so on. What about capital? Capital goods are all the man–made aids to producing, storing, transporting, and distributing goods and services. Capital goods differ from consumer goods in that the latter satisfy wants directly, while the former do so indirectly by facilitating the production of consumer goods. It should be noted that capital as defined here does not refer to money. Money, as such, produces nothing.

The term labor refers to the physical and mental talents of humans used to produce goods or services (with the exception of a certain set of human talents, entrepreneurial skills, which will be considered separately because of their special significance). Thus the services of a factory worker or an office worker, a ballet dancer or an astronaut all fall under the general heading of labor.

What is the author's main purpose in writing this passage? 

A. To explain the concept of labor

B. To criticize certain uses of capital.

C. To contrast capital goods and consumer goods

D. To define economic resources

Theo thuyết lượng từ ánh sáng thì năng lượng của

A. các phôtôn trong chùm sáng đơn sắc bằng nhau

B. một phôtôn phụ thuộc vào khoảng cách từ phôtôn đó tới nguồn phát ra nó

C. một phôtôn bằng năng lượng nghỉ của một êlectrôn

D. một phôtôn tỉ lệ thuận với bước sóng ánh sáng tương ứng với phôtôn đó

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.

THE SAVANNAH

The tourist looking at the African savannah on a summer afternoon might be excused for thinking that the wide yellow grass plain was completely deserted of life, almost a desert. With only a few small thorn trees sticking out through the veldt, there seems to be almost no place for a living creature to hide.

However, under those trees you might find small steenbok, sleeping in the shade, and waiting for the night to fall. There may even be a small group of lions somewhere, their bodies exactly the same shade as the tall grass around them. In the holes in the ground a host of tiny creatures, from rabbits and badgers to rats and' snakes are waiting for the heat to finish.

The tall grass also hides the fact that there may be a small stream running across the middle of the plain. One clue that there may be water here is the sight of a majestic Marshall eagle circling slowly over the grassland. When he drops, he may come up with a small fish, or maybe a grass snake that has been waiting at the edge of a pool in the hope of catching a frog.

The best time to see the animals then, is in the evening, just as the sun is setting. The best time of the year to come is in late September, or early August, just before the rains. Then the animals must come to the waterholes, as there is no other place for them to drink. And they like to come while it is still light; so they can see if any dangers are creeping up on them.

So it is at sunset, and after the night falls, that the creatures of the African veld rise and go about their business.

The phrase "a host of" in paragraph 2 is closest in meaning to

A. a large number of

B. only a few

C. a group of 

D. a gang of

Học sinh lớp 12A đang thảo luận kế hoạch tổ chức liên hoan chia tay sau khi tốt nghiệp phổ thông. Bạn nào cũng hăng hái phát biếu ý kiến. Đây là việc các bạn đang thực hiện

A. Quyền tự do của học sinh trong lóp

B. Quyền bình đẳng trong hội họp.

C. Quyền dân chủ trực tiếp.

D. Quyền dân chủ gián tiếp.

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

  Wind, water, air, ice and heat all work to cause erosion. As the wind blows over the land, it often (26) _______ small grains of sand. When these grains of sand strike against solid rocks, the rocks are slowly worn away. In this way, even very hard rocks are worn away by the wind.

  When particles of rocks or soil became loosened in any way, running water carries them down the hillsides. Some rocks and soil particles are carried into streams and then into the sea.

  Land that is covered with trees, grass and other plants wears away very slowly, and so loses very (27) _______ of its soil. The roots of plants help to (28) _______ the rocks and soil in place. Water that falls on grasslands runs away more slowly than water that falls on bare ground. Thus, forests and grasslands help to slow down erosion.

          Even where the land is (29) _______ covered with plants, some erosion goes on. In the spring, the (30) _______  snow turns into a large quantity of water that then runs downhill in streams. As a stream carries away some of the soil, the stream bed gets deeper and deeper. After thousands of years of such erosion, wide valleys are often formed.

Điền ô số 29

A. thinly

B. strongly

C. thickly

D. scarcely

Hợp chất X có công thức C8H14O4. Từ X thực hiện các phản ứng (theo đúng tỉ lệ mol):

(a) X + 2NaOH ® X1 + X2 + H2O (b) X1 + H2SO4® X3 + Na2SO4

(c) nX3 + nX4 ® nilon-6,6 + 2nH2O (d) 2X2 + X3® X5 + 2H2O

Phân tử khối của X5 là

A. 202

B. 174

C. 198

D. 216