单项选择题
A.at the start of spring，when the Sun is nearly over the equator
B.only when the Sun and Moon are on the same sides of the Earth and are nearly in line
C.when the Sun and Moon are at approximately 90°to each other，as seen from the Earth
D.when the Sun，Moon，and Earth are nearly in line，regardless of alignment order
单项选择题 In which month will the equatorial counter current be strongest? （）
单项选择题 In mid-ocean，the characteristics of a wave are determined by three factors. What is NOT one of these factors?（）
单项选择题 Generally speaking，a ship steaming across the North Pacific from Japan to Seattle is likely to experience（）.