for those who don't smoke,it is much easier not to start smoking than it is to quit it.中的it is省
问题描述：
for those who don't smoke,it is much easier not to start smoking than it is to quit it.中的it is省
to quit it前的it
答
前面已经有it is了,已经表达了同一个主语,所以可以去掉后面的it is；而且去掉也显得语句更为流畅明了.