96. If they didn't live in the area affected by air pollution, they wouldn't have breathing problems.

if 2: if + QKĐ, S + would / could + V1 

97. I asked her if Pyramids in Egypt attracted a lot of tourists every year.

S+ asked + O + if/whether + S+ V (lùi thì)

HTĐ --> QKĐ

98. Nga said that she would hand in her assignment to the teacher the next day..

S + said+(that) + S+ V (lùi thì)

will --> would 

tomorrow --> the next day / the following day 

99. Mr. John said that they didn't open the library that day.

S + said + (that) + S+ V (lùi thì)

HTĐ --> QKĐ

today --> that day 

100. If I had free time, I could go somewhere.

If 2 :If + QKĐ, S + would / could + V1 

`color{orange}{~MiaMB~}`