There are many things that a pilot must do before the flight. They must check out weather conditions on the flight path and around the landing area. They also have to check flight plans, fill in forms and do a lot of paperwork. Before takeoff pilots brief their crew and do a complete check of the airplane to see if everything works the way it should.

Pilots must calculate how much fuel they have to take with them.

(Adapted from http://www.english.online.at/travel/airlane-pilot)

“Must” in bold type can be correctly replaced by: