题目

In our school there are 2,000 students, four fifths of _________ are boys. A. which           B. whom               C. which               D. who 答案：B分子式为C3H4Cl2链状有机物的同分异构体共有(不考虑顺反异构) A．4种    B．5种    C．6种  D．7种