I refuse to believe a word of it, it's a cock-and- _______ story. 

A. bull 

B. hen 

C. duck 

D. goose 

The authorities _____ actions to stop illegal purchase of wild animals and their associated products effectively. However, they didn't do so. 

A. should have taken 

B. needed have taken 

C. must have taken 

D. had to take

Thủy phân hoàn toàn 1 mol pentapeptit X mạch hở thì thu được 3 mol glyxin, 1 mol alanin và 1 mol valin. Khi thủy phân không hoàn toàn X thì trong sản phẩm thấy có các đipeptit Ala-Gly, Gly-Ala và tripeptip Gly-Gly-Val. Công thức của X và phần trăm khối lượng của N trong X là:

A. Gly-Gly-Val-Gly-Ala; 15%.

B. Ala-Gly-Gly-Val-Gly; 11,2%

C. Gly-Ala-Gly-Gly-Val; 20,29%.

D. Gly-Ala-Gly-Gly-Val; 19,5%.

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.

We arrived at the conference. Then we realized that our reports were still at home. 

A. No sooner had we realized that our reports were at home than we arrived at the conference

B. Only after we arrived at the conference did we realize that our reports were still at home. 

C. Not until we arrived at the conference that we realized that our reports were still at home. 

D. Hardly had we arrived at the conference when we realized that our reports were still at home.