单项选择题
The changes in the channel’s sands and buoys on this coast are （） this chart can not be considered as a safe guide of the channel．
A.frequent B.so frequent C.frequent that D.so frequent that
单项选择题 （）chart 3994，positions read from this chart should be shifted 0.03 minutes Northward．
单项选择题 A Mercator chart is a （）.
单项选择题 A revised print of a chart is made （）.
