I)
1 . smoking `=>` to smoke
2 . using `=>` to use
3 . picking `=>` to pick
4 . came `=>` to come
5 . to wait `=>` waiting
6 . had had `=>` were having
7 . pollute `=>` pollution
8 . am `=>` were
9 . pollute `=>` polluting
10 . occur `=>` occured
11 . had went `=>` went
12 . waited `=>` wait
13 . had taken `=>` took
14 . but `=>` so
15 . most `=>` almost
16 . hasing `=>` having
17 . to wait `=>` waiting
18 . visiting `=>` to visit
19 . be `=>` bỏ "be"
20 . possibly `=>` possible