Dual angle-airflow sensors (alpha vanes) provide angle-of-attack information to the stall warning system, autothrottle, autopilot and autoslats and are anti iced:
A.A.By actuating the LEFT or RIGHT FWD window heat switch.
B.B.Whenever wing anti-ice is being used.
C.C.Whenever the alternate static ports are heated.
D.D.By independent 115V AC heating elements, controlled by the Probe Heat switches.
正确答案是D