进行生物工程设计时，下表各组所选择的实验材料与实验目的配置错误的组是

A．1

B．2

C．3

D．4

(2014·南昌第二中学高三检测)We must keep our room clean，for dirt and disease go________，you know.

A．hand in hand　

B．step by step

C．from time to time　

D．one after another