单项选择题
A.Being mroe than 25 miles from shore
B.Only at night when it‟s dark
C.Being more than 6 miles from shore
D.Never
单项选择题 Which kind of fog is also named as ground fog?（）
单项选择题 Normally the mariners care more about the（）of tide.
单项选择题 The International Association of Lighthouse authorities (IALA) buoyage system “A” uses some types of marks to distinguish safe navigation? Which type(s) does(do) not belong to the system?（）