单项选择题
Periodic publications notifying changes in，or additions to，previously published navigational data are（）.
A.Supplements B.Annual Summary C.Navigational Warnings D.Notices to Mariners
单项选择题 On the high seas，a fog signal consisting of one prolonged blast followed by four short blasts would indicate the presence of a（）.
单项选择题 On the approach of a warm front the barometric pressure usually（）.
单项选择题 On a nautical chart，the inner ring of a compass rose indicates（）.
