单项选择题
River currents tend to（）.
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
单项选择题 Priming of the tides occurs（）.
单项选择题 One of the causes of ocean currents is density differences in the water. This is true because （）.
单项选择题 Neap tides occur when the（）.
