a.
1.  √ (correct)
2. many => much
3. much => many
4. √ (correct)
5. traffic jams => traffic jam
b.
1. There isn't much entertainment in the country.
2. There is lots of fresh air and nature in the country.
3. There are not enough sport facilities in the country.
4. He doesn't think there is enough room for all people in the city.
5. My mom doesn't like the city because there are too many vehicles there.