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

此题考查的是被动语态，由be+过去分词。算盘是人发明的，它是动作的承受者。发明在过去，故用was invented,选C。