1. (It is dangerous.) The faster you drive, the more dangerous it is.

Answer:

The faster you drive, the more dangerous it is to yourself and others.

2. (Your marks will be good.) The harder you work, the better your marks will be.

Answer:

The harder you work, the more likely you are to get good marks.

3. (I feel fit.) The more I exercise, the fitter I feel.

Answer:

The more I exercise, the stronger and healthier I feel.

4. (We'll get there late.) The later we leave, the later we'll get there.

Answer:

The later we leave, the less time we'll have to get there.

5. (It is quiet.) The further we are from the city, the quieter it is.

Answer:
The further we are from the city, the less noise and pollution there is.

6. (The roads became busy.) The nearer we got to the city centre, the busier the roads became.

Answer:
The nearer we got to the city center, the more congested the traffic became.