Problem: How does the sentence end?

Rachel gave a reward to Monica for doing a great job on the account, since 
Answer: Rachel was a good boss.

Problem: How does the sentence end?

Robert has many tattoos on his body, while Aaron has none, because 
Answer: Robert is an atheist.

Problem: How does the sentence end?

Justin attended all of the wild parties without Brett, because 
Answer: Brett wanted to be a homebody.

Problem: How does the sentence end?

Katrina taught Lindsey how to pick up girls because 
Answer:
Katrina was quite skilled at it.