What is the procedure for when the flag is flown at half-mast?

a.
The flag is hoisted to the top of the staff when raised and before being lowered.

b. The flag is hoisted to the top of the staff when raised but not when being lowered.

c. The flag is hoisted to the top of the staff when lowered but not when raised.

d. The flag is not hoisted to the top of the staff when raised