In my opinion，life in the twenty－first century is much easier than .
A. that used to be
B. it is used to
C. it was used to
D. it used to be
网友回答
A. that used to be
B. it is used to
C. it was used to
(答案→)D. it used to be
解析：表示 “过去常常……”用“used to do”。本题中“be”为连系动词，不是实义动词，不能省略。