眼动脉是由哪根动脉发出的第几分支（）。
A.颈内，第一
B.颈外，第三
C.颈总，第二
D.椎动脉，颅内
E.颈内，第三
参考答案：A
什么是液压控制元件？
For a floating vessel，the center of buoyancy and the metacenter are in the line of action of the buoyant force（）.
A.only when there is positive stability
B.only when there is negative stability
C.only when there is neutral stability
D.at all times
