According to the regulations for life boat falls，which action must be taken at 30-month intervals?（）

单项选择题A sheave is a（）.

A.grooved wheel in a block
B.line to hold a lifeboat next to the embarkation deck
C.partial load of grain
D.seaman's knife

单项选择题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

单项选择题A person referring to the stern sheets of a lifeboat is speaking of（）.

A.the line attached to the tack of the lugsail
B.the emergency rudder
C.a canvas awning
D.the aftermost seating

单项选择题（）is used for heaving up and slacking away the anchor and chain.

A.A winch
B.A windlass
C.A deck crane
D.A lifeboat engine

单项选择题Frapping lines are fitted to lifeboat davits to（）.

A.secure the lifeboat in the davits when in the stowed position
B.bring the lifeboat close along the rail in the embarkation position
C.give the occupants a safety line when the boat is being lowered from the embarkation level
D.reduce the swinging of the lifeboat at the embarkation level