单项选择题
How is the annual rate of change for magnetic variation shown on a pilot chart?（）
A.Gray lines on the uppermost inset chart B.Red lines on the main body of the chart C.In parenthesis on the lines of equal magnetic variation D.Annual rate of change is not shown
单项选择题 How is a safe water mark，that can be passed close aboard on either side，painted and lighted?（）
单项选择题 How does the effect known as “bank suction” act on a single-screw vessel proceeding along a narrow channel?（）
单项选择题 How does foam extinguish an oil fire?（）
