For a controlled flight before departure, a flight plan must be filed at least:
a. 50 minutes before off-block time
b. 60 minutes before departure
c. 10 minutes before departure
d. 30 minutes before off-block time
a. 50 minutes before off-block time
b. 60 minutes before departure
c. 10 minutes before departure
d. 30 minutes before off-block time