物种甲某些性状的进化引起物种乙相应性状的进化，物种乙这些性状进化的本身反过来又影响到物种甲相应性状的进化，此现象称为______。
参考答案：协同进化
根据中文意思选择正确的短语补全句子。
1. His math teacher is _____________ (又高又瘦).[ ]
A. tall and thin
B. tall and strong
C. tall and kind
2. My P. E. teacher is _____________ (活跃的). [ ]
A. quiet
B. funny
C. active
3. The girl is _____________ (年轻漂亮). [ ]
A. young and kind
B. young and pretty
C. young and smart
4. Our principal is _____________ (年老和蔼的). [ ]
A. old and kind
B. young and funny
C. old and strict
