Gliding Flight Is Different from Normal Flapping Flight in That

Gliding flight is different from normal flapping flight in that

A) most of the lift is generated by the upstroke.
B) both downstroke and upstroke generate large amounts of lift.
C) the wings are held close to the body on the downstroke to reduce drag.
D) it requires thermals to remain airborne.
E) gliding flight is energetically more efficient.