I usually get nervous before ______ a big exam. [ ]

A. taking

B. takes

C. taken

D. took

麻黄的功效是

A．发汗解表，宣肺平喘，温中止呕

B．发汗解表，宣肺平喘，利水消肿

C．发汗解表，宣肺平喘，温经通脉

D．发汗解表，宣肺平喘，芳香化湿

E．发汗解表，宣肺平喘，散寒止痛