—When shall we send the washing machine to you, Mrs. Read?
— on Thursday on Friday, please. I'll be at home then.
A:Either; or
B:Neither; nor
C:Both; and
计算:
写出下列概念的象征义:
①灰色的幔:____。
②苍蝇、蚊子和蝉儿:____。
③大雷雨:____。
如图所示的电路,当开关S闭合后( )