单项选择题
On a Mercator chart，1 nautical mile is equal to（）.
A.1 minute of longitude B.1 degree of longitude C.1 minute of latitude D.1 degree of latitude
单项选择题 Every chart is liable to be incomplete（）.
单项选择题 Charts showing the coast of Mexico are produced by the United States（）.
单项选择题 A chart with a scale of 1:80，000 would fall into the category of a（）.
