X, Y là hai hợp chất hữu cơ đơn chức phân tử chỉ chứa C, H, O. Khi đốt cháy X, Y với số mol bằng nhau hoặc khối lượng bằng nhau đều thu được CO₂với tỉ lệ mol tương ứng 2 : 3 và H₂O với tỉ lệ mol tương ứng 1 : 2. Số cặp chất X, Y thỏa mãn là

A. 4.                     

B. 6.                     

C. 5.                     

D. 3

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 our reports were still at home.

A. We arrived at the conference and realized that our reports are still at home. 

B. It was until we arrived at the conference that we realize our reports were still at home. 

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

D. Not until had we arrived at the conference we realized our reports were still at home.

Cho các chất sau : stiren, glixerol, axit acrylic, anilin, saccarozơ, phenol. Số chất làm nước brom bị mất màu là

A. 2.

B. 3.

C. 5.

D. 4.