Which of the Following Statements Gives the Main Reason That

Multiple Choice

Which of the following statements gives the main reason that night-time radio broadcasts can be sent over long distances?

A) Radio waves propagate more efficiently through cooler, high-density air.
B) Radio stations put out more power at night.
C) The low D-level region of the ionosphere is weaker at night.
D) There is less interference because many radio stations do not broadcast at night.