203. Hawks eat more field _____ than _____ . We should take good care of them and not kill them

A．mouse… Chicken

B．mice… chicken

C．mouse… Chickens

D．mice… Chickens

单纯性下肢静脉曲张的主要病因是()。

A．妊娠

B．动静脉瘘

C．深静脉受阻

D．静脉壁发育不良

E．腹内压增高