Trường hợp nào sau đây không xảy ra phản ứng hoá học? 

A. Sục khí C l 2 vào dung dịch F e C l 2 . 

B. Sục khí  H 2 S  vào dung dịch  C u C l 2 . 

C. Sục khí  H 2 S  vào dung dịch  F e C l 2 . 

D. Cho Fe vào dung dịch  H 2 S O 4  loãng, nguội. 

He / suffer / rare tropical disease / which / contracted / while / Africa

A. He still suffers from a rare tropical disease which contracted while he was in Africa.

B. He still suffers from a rare tropical disease which he contracted while he was in Africa.

C. He suffers from a rare tropical disease which he contracts while in Africa.

D. He suffers from a rare tropical disease which was contracted while he is in Africa.

Cho cosα = - 2 / 3 với π < α < 3π/2. Giá trị cotα là