Ⅰ级易燃气体的爆炸下限为（）。

A.<5%

B.<10%

C.≤5%

D.≤10%

A sea anchor is（）.

A.a heavy anchor with an extra long line used to anchor in deep water

B.a cone shaped bag used to slow down the wind drift effect

C.a padeye to which the sea painter is made fast

D.made of wood if it is of an approved type