[单选题]As far as I know, the robot that can sweep the floor（ ）in the 1980s.
A
is invented
B
invented
C
was invented
D
has invented
正确答案：C
题目解析
本题考查被动语态。本句中that can sweep the floor作定语从句修饰本句主语 the robot，the robot与invent构成被动关系。is invented是一般现在时的被动语态，was invented是一般过去时的被动语态，has invented是现在完成时态。本句描述的事情发生在20世纪80年代，故用一般过去时的被动语态。故选C。
