纵桁和上翼面蒙皮构成通风通道。通风通道在中央油箱内有排放浮子活门.
A.Stringers and the upper wing skin are called vent channels; The vent channels go through drain float valves in the center tank. B.Stringers and the upper wing skin are composed of the vent channels. The vent channels got exhaust float valves from the center tank. C.Stringers and the upper wing skin make the vent channels. The vent channels have drain float valves in the center tank.正确答案C
