What does Milton mean in line 7?

LINE 7 IS
Thousands at his bidding speed7
And post o'er Land and Ocean without rest:
They also serve who only stand and wait."

ANSWER OPTIONS
A "Does God want me to work in the day when I work better at night?"
B "Does God want me to work in the day?"
C "Does God demand work worthy of a day's labor when he has taken my vision?"
D "Does God want me to work at night?"