9. The period of incomplete darkness when the upper limb of the sun is below the visible horizon, and the center of the sun is not more than 6° below the celestial horizon. It is:
(A) Civil twilight
(B) Nautical twilight
(C) Astronomical twilight
(D) Global Horizon twilight
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統計: A(417), B(97), C(59), D(77), E(0) #2999683
統計: A(417), B(97), C(59), D(77), E(0) #2999683