Thismachine,

问题详情：

This machine, ______for many years, is still working perfectly.

A. after which I have looked         B. which I have looked after

C. that I have looked after           D. I have looked after

【回答】

B. which I have looked after 构成一个非限制*定语从句.

知识点：定语从句

题型：选择题