Có các chất: brom, hiđro clorua, iot, natri clorua, khí cacbonic, nitơ, oxi, clo. Hãy cho biết chất nào là khí độc, màu vàng lục.

Khi đi từ bờ này sang bờ kia, theo phương vuông góc với bờ, hướng của vận tốc thuyền đối với bờ hợp với bờ 1 góc xấp xỉ ?

A.  72 °

B.  18 °

C.  17 °

D. 43 °

Cho một phản ứng hạt nhân tỏa năng lượng. Gọi Δ m t r là tổng độ hụt khối lượng các hạt nhân trước phản ứng; Δ m s là tổng độ hụt khối lượng các hạt nhân sau phản ứng. c là tốc độ ánh sáng trong chân không. Năng lượng tỏa ra của phản ứng là Q(Q>0) được tính bằng biểu thức

A.  Q = Δ m t r − Δ m s c 2

B.  Δ m t r − Δ m s c

C.  Q = Δ m s − Δ m t r c 2

D.  Q = Δ m s − Δ m t r c

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

    Millions of people are using cell phones today. In many places, it is actually considered unusual not to use one. In many countries, cell phones are very popular with young people. They find that the phones are more than a means of communication - having a mobile phone shows that they are cool and connected.

    The explosion in mobile phone use around the world has made some health professionals worried. Some doctors are concerned that in the future, many people may suffer health problems from the use of mobile phones. In England, there has been a serious debate about this issue. Mobile phone companies are worried about the negative publicity of such ideas. They say that there is no proof that mobile phones are bad for your health. On the other hand, medical studies have shown changes in the brain cells of some people who use mobile phones. Signs of change in the tissues of the brain and head can be detected with modern scanning equipment. In one case, a traveling salesman had to retire at young age because of serious memory loss. He couldn't remember even simple tasks. He would often forget the name of his own son. This man used to talk on his mobile phone for about six hours a day, every day of his working week, for a couple of years. His family doctor blamed his mobile phone use, but his employer's doctor didn't agree.

          What is it that makes mobile phones potentially harmful? The answer is radiation. High-tech machines can detect very small amounts of radiation from mobile phones. Mobile phone companies agree that there is some radiation, but they say the amount is too small to worry about. As the discussion about their safety continues, it appears that it's best to use mobile phones less often. Use your regular phone if you want to talk for a long time. Use your mobile phone only when you really need it. Mobile phones can be very useful and convenient, especially in emergencies. In the future, mobile phones may have a warning label that says they are bad for your health. So for now, it's wise not to use your mobile phone too often

The word “potentially” in the passage most closely means ______.

A. possibly

B. privately

C. certainly

D. obviously

Vẽ hình lục giác đều, hình vuông, tam giác đều cùng nội tiếp đường tròn (O; R) rồi tính cạnh của các hình đó theo R.

Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best combines each pair of sentences in the following questions.

Mary knew how busy I was. She offered to help me.

A. Because Mary knew my business, she offered to help me. 

B. Knowing how busy I was, Mary offered to help me. 

C. Mary knew how I was busy and offered to help me. 

D. Having known how busy I was, Mary offered to help me.

Chất hữu cơ mạch hở X có công thức C₈H₁₅O₄N. Cho m gam X tác dụng với lượng dư dd NaOH, thu được (m + 1) gam muối Y của amino axit và hỗn hợp Z gồm hai ancol. Giá trị của m là

A. 15,75

B. 7,27

C. 94,50

D. 47,25