Question: I ran out of breath. What is the cause?

Answer: I climbed several flights of stairs.

Question: The woman hummed to herself. What is the cause?

Answer: She was in a good mood.

Question: I excused myself from the group. What is the cause?

Answer: My phone rang.

Question: I received a package in the mail. What is the effect?

Answer:
The package triggered my curiosity.