Problem: Continue the following story.

James chose to buy the guitar and leave the piano because that is what he can afford. The 
Here's how I want to continue it: guitar is cheap.

Problem: Continue the following story.

William heard Craig needed a caretaker for a baby, so 
Here's how I want to continue it: William volunteered to help with it.

Problem: Continue the following story.

The flowers on the trees caused Mary to sneeze a lot but not Jennifer because 
Here's how I want to continue it:
Jennifer doesn't have an allergy to tree pollen.