单项选择题
Carbon dioxide as a fire fighting agent has which advantage over other agents? （）
A.It causes minimal damage B.It is safer for personnel C.It is cheaper D.It is most effective on a per unit basis
单项选择题 Before sailing for a foreign port，what document must you get?（）.
单项选择题 Before leaving port on an ocean tow，a tug captain should assure himself of all the following EXCEPT（）.
单项选择题 Before any machinery is put in operation，you should（）.
