— Jimmy had a lot of parties recently.

— Yes, that might       why he didn’t do well in the test.

A．sum up

B．add up to

C．account for

D．count on

单一导线布设有（）形式

A.闭合导线

B.附合导线

C.支导线

D.经纬仪导线

E.全站仪导线