Problem: How does the sentence end?

Robert lent the book to Ian for the reason that 
Answer: Robert already read the book.

Problem: How does the sentence end?

Emily avoided getting the hypothermia that Maria succumbed to, because 
Answer: Maria had worn inadequate clothing.

Problem: How does the sentence end?

Steven was better at making pastries than Donald because 
Answer: Donald tended to overwork the dough.

Problem: How does the sentence end?

Deciding on a new color of paint for the room was difficult for Dennis but came natural to Ian, since 
Answer:
Ian was decisive by nature.