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

Years ago there were many social rules and etiquette procedures (16)________introductions. Some formal introductions between two people were (17)_________by letter by third party. A person had to be very careful to weigh the importance of social class or status, age, and gender when deciding (18)                 person should be presented or introduced to the other person first. (19)_________, times have changed, and most of the social rules about introducing older people to younger ones, women to men, and those in higher positions to those in lower positions have changed, too. Many people now feel much more (20)                         about making introductions.In most situations, handshaking is (21)               , but these days it is more often done than not- especially in formal social or business settings. It’s very common for one person (or both) to (22)                        a hand when meeting someone. If you are in this situation, and you are offered a hand toshake, you should grasp it firmly and shake it briefly. People often tend to make some (23)                  about someone (24)_______to their handshakes, so make sure yours is not too weak or limp, not too hard, and not too long-lasting. (25)                       should be firm and brief.

Question 21

A.optional

B.compulsory

C.private

D. formal

Cho 80 gam metan phản ứng với clo có chiếu sáng thu được 186,25 gam hỗn hợp X gồm 2 chất hữu cơ Y và Z. Tỉ khối hơi của Y và Z so với metan tương ứng là 3,15625 và 5,3125. Để trung hòa hết khí HCl sinh ra cần vừa đúng 8,2 lít dung dịch NaOH 0,5M. Hiệu suất của phản ứng tạo Y và Z lần lượt là

A. 50% và 26%

B. 25% và 25%

C. 30% và 30%

D. 30% và 26%