Problem: Continue the following story.

After the knee surgery he tried to use walker but switched to wheelchair, because the 
OPTIONS:
- walker was more comfortable.
- wheelchair was more comfortable.
Here's how I want to continue it: wheelchair was more comfortable.

Problem: Continue the following story.

It was easy to see that Erin but not Sarah was a good waitress because 
OPTIONS:
- Erin received a few tips on a daily basis.
- Sarah received a few tips on a daily basis.
Here's how I want to continue it: Erin received a few tips on a daily basis.

Problem: Continue the following story.

Christine praised Carrie about their abs, because 
OPTIONS:
- Christine had been working out more in the gym.
- Carrie had been working out more in the gym.
Here's how I want to continue it:
Carrie had been working out more in the gym.