Sure! Here are the completed sentences:

1. This gym is less convenient than the one near my house.
→ This gym **is not as** convenient as the one near my house.

2. Mount Everest is higher than any other mountain in the world.
→ Mount Everest **is the highest** mountain in the world.

3. His writings have influenced modern Christian theology.
→ Modern Christian theology **has been influenced by** his writings.

4. The group plans to establish an import business.
→ The group plans to **set up** an import business.

5. His father is the most capable man in the office.
→ No other man in the office is **more** capable than his father.

6. The product quickly made an impact on the market.
→ The product quickly **influenced** the market.

7. Jonah had obviously made an effort to put on smart clothes for the occasion.
→ Jonah had obviously made an effort to **dress up** for the occasion.

8. Losing weight is not so easy as putting on weight.
→ Losing weight is **difficult** compared to putting on weight.