Rewrite the following sentence into direct speech: "The headmaster advised us to switch off the fans when we leave the class."
a) "Switch off the fans when you leave the class," advised the headmaster.
b) "Fans should be turned off when leaving the class," said the headmaster.
c) "Leave the class and turn off the fans," instructed the headmaster.
d) "Fans off upon class departure," the headmaster commanded.