1.Changes within the (chemist) structure of the single gemes may be induced by exposure to radiation and extreme temperatures.

请问chemist应该怎么改呢？

2. In the nineteenth century, north American locomotives ran on hardwood fuel, which was inexpensive and plentiful (in) the time.

in 是不是要改为during？

3. Globally,( the) 1990s stood (out) as the (warmest) decade for (what) we have weather records.

what为什么错了？应该怎么改？

恳请指教，谢谢！！！

1,chemist->chemical

2,->at the time

3,what->which