They insulate against cold air. They optimize solar heating. They reduce radiant cooling. They act as a windbreak.
I gave my students this multiple choice question: Which of the following is the primary way that evergreen trees planted on the north and west sides of residences in Massachusetts help reduce winter heating costs?

Only one answer is correct among these 4 choices:
- They insulate against cold air.
- They optimize solar heating.
- They reduce radiant cooling.
- They act as a windbreak.

Could you tell me which one is correct?

They act as a windbreak.