()、()和()均能在特定条件下导致群落结构发生改变。
参考答案:捕食;寄生;疾病
The spokesman said that this was a(n) ____ negotiation (谈判) because it solved a lot of problems between
the two sides. [ ]
A. attractive
B. defensive
C. protective
D. productive
止回阀是装在()的一个单流阀。
A、外岩心筒上端
B、内岩心筒上端
C、外岩心筒下端
D、内岩心筒下端