On all vessels equipped with refrigeration units of over 20 cubic foot capacity, （）.

A. a gas mask suitable for protection against each refrigerant used, or a self contained breathing apparatus must be provided
B. it is the sole responsibility of the chief engineer to ascertain that all members of the engineering department are familiar with the use of gas masks or breathing apparatus
C. spare charges shall be carried for at least 50% of each size and variety of gas masks and/or self contained breathing apparatus
D. all of the above