搜题请搜索小程序“爱下问搜题”
问题 单项选择题

流行病学实验分为

A．临床试验和社区试验

B．治疗试验、干预试验、预防试验

C．临床试验和预防试验

D．前瞻性试验和回顾性试验

E．现场试验和实验室试验

答案

参考答案：A

选择题

—I don't know which to buy.  Can you give me some advice?

—You _______ try on this T-shirt. It looks nice. [ ]

A. had not better

B. had better not

C. had better

D. had better to

查看答案
单项选择题

营养液配方中常使用（）氮肥，所造成的不良影响较容易克服。

A.NH4+-N

B.NO3--N

C.酰胺态氮

D.尿素
查看答案