An example of a modern anchor which has a stock is a(n)（）.

An integral part of a blowout preventer that serves as the closing element on an open hole，and whose ends do not fit around the drill pipe but seal against each other and shut off the space below completely is the（）.

The function of the bypass valve on the self-contained breathing apparatus is to（）.

In relation to cargo gear，what does SWL mean?（）.

In ship construction，frame spacing is（）.

The series of valves used to control the return flow in well control operations is called the（）.

The bypass valve on a self-contained breathing device should be opened if（）.

If a gasoline engine turns over freely but will not start，the cause is generally（）.

As the propeller turns，voids are formed on the trailing and leading edges of the propeller blades causing a loss of propulsive efficiency，pitting of the blades，and vibration. These voids are known as（）.

On a ship，a door that is required to be marked KEEP CLOSED is designed to（）.