单项选择题
A.have lows lower than normal and highs higher than normal B.have lows higher than normal and highs lower than normal C.are unpredictable D.occur in the spring of the year
A.Pick up speed where the channel widens B.Run slower in the center of the channel C.Hug the inside of a bend D.Cause the greatest depth of water to be along the outside of a bend
A.at times of new and full Moon B.when the Earth，Moon，and Sun are lying approximately on the same line C.when the Moon is between first quarter and full and between third quarter and new D.when the Moon is between new and first quarter and between full and third quarter