劳动者以辞职的形式解除劳动合同必须提前（）天通知。

A．10

B．15

C．30

D．45

E．60

Geographic range is the maximum distance at which a light may be seen under（）.

A.existing visibility conditions，limited only by the curvature of the Earth

B.perfect visibility conditions，limited only by the curvature of the Earth

C.existing visibility conditions，limited only by the intensity of the light

D.perfect visibility conditions，limited only by interference from background lighting