-What do you think of the music teacher?

-       she is an elegant lady, she can be extremely difficult to work with.

A．While

B．When

C．Even if

D．As

实验设计的四原则是（）

A.收集、整理、分析、结论

B.齐同、对照、重复、随机

C.设计、操作、计算、推断

D.对照、随机、操作、归纳

E.对照、随机、操作、汇总