A. There are several types of hatch covers on board ship.
B. There are several types of hatches on board ship.
C. There is one type of hatches on board ship.
D. There is one type of hatch covers on board ship.

A. The work of opening and closing hatches is usually done by crew members.
B. The work of opening and closing hatch covers is usually done by crew members.
C. The work of opening hatch covers is usually done by crew members.
D. The work of closing hatch covers is usually done by crew members.