Apparent wind speed blowing across a vessel under tow can be measured by a(n)（）.

A.during the day，three balls in a vertical line
B.during the day，three shapes，the highest and lowest being balls and the middle being a diamond
C.when making way at night，two all-round red lights，sidelights，and a sternlight
D.when making way at night，masthead lights，sidelights，and a sternlight

A.a vessel restricted in her ability to maneuver
B.a vessel not under command
C.a vessel engaged in fishing
D.a vessel constrained by her draught