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：句意：我认为，生活在21世纪要比过去容易得多。 than 引导的是一个比较从句，同一个人或物，现在和过去两个不同的时间进行对比时，应该用人称代词，因此要有主语it，而used to be 是“曾经的那个样子”之意。故选D。