1. We usually visit museums when we have leisure time (enjoy)

  →We enjoy visiting museums when we have leisure time.

2. He uses all his free time to look after his garden. (spends)

  →He spends all his free time looking after his garden.

3. Hung drives more carefully than his brother. (carefully)

  →Hung's brother drives less carefully than him.

4. A sports car goes faster than an ordinary car. (slowly)

  →An ordinary car goes more slowly than a sports car. 

5. No one has opened that box for the past 100 years

  →The box hasn't been opened for the past 100 years.