The word "random" (Line 3, Para. 3) is closest in meaning to______.

A．Although birds preen, the feather wears out.
B．Two processes are involved in molting.
C．When most feathers have been replaced, then the molt is completed.
D．A bird seems unwell when molting.

A．constantly preening and caring for their remaining feathers
B．dropping flight feathers on both sides at the same time
C．adjusting the angle of their flight to compensate for lost feathers
D．only losing one-third of their feathers