Question

--When _____ the abacus _____?   -- In the sixth century by the Chinese people.

A．is, invented

B．did, invent

C．was, invented

D．does, invent

Answer 1

C

此題考查的是被動語態，由be+過去分詞。算盤是人發明的，它是動作的承受者。發明在過去，故用was invented,選C。