单项选择题
Opposition occurs when（）.
A.the Sun，Earth，and Moon are at right angles B.the Sun's declination is 0°and is moving south C.an inferior planet is at the maximum angle to the line of sight to the Sun D.the Earth is between a planet and the Sun
单项选择题 On mid-ocean waters，the height of a wind-generated wave is not affected by the（）.
单项选择题 Mars will not be visible（）.
单项选择题 It is difficult to determine which limb of the Moon is fully illuminated（）.
