Thực hiện các thí nghiệm sau:

(a) Cho P₂O₅ vào nước;                                 (b) Sục hỗn hợp khí NO₂ và O₂ vào nước;

(c) Sục khí CO₂ vào dung dịch Na₂SiO₃;       (d) Cho P vào dung dịch HNO₃ đặc, nóng.

Số thí nghiệm tạo ra axit là

A. 1.  

B. 2.  

C. 3.  

D. 4.

Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.

It had been snowing all day. A great many people managed to get to the end-of-term concert.

A. Very few people indeed were prevented from getting to the end-of-term concert by the heavy snow

B. Since there had been snow all day long, it wasn’t easy for people to get to the end-of-term concert

C. As it had been snowing heavily all day, a great many people just could not get to the end-of-term concert

D. A lot of people did get to the end-of-term convert in spite of the snow that fell all day

\(A=\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{49.50}\)

\(A=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{49}-\dfrac{1}{50}\)

\(A=1-\dfrac{1}{50}\)

\(A=\dfrac{49}{50}\)