Problem: How does the sentence end?

To get a better clean, Mark used the sponge instead of the towel, because the 
Answer: towel got dirtier faster.

Problem: How does the sentence end?

Betty had yellowed teeth while Erin had perfectly teeth; 
Answer: Erin offered her some whitening toothpaste.

Problem: How does the sentence end?

The disease was more prevalent in the nursing home than in the school because the people in the 
Answer: nursing home were older.

Problem: How does the sentence end?

Lawrence wanted to teach calculus while Derrick wanted to teach comic strips because 
Answer:
Derrick was a fun teacher.