Answer
“Magnetic variation information is stored in each IRS memory; it is applied to
the true heading calculated by the respective IRS” is not generally correct but
it is better than the other options.
There is no
input from the gyro compass detector (flux valve) so “The main directional gyro
which is coupled to the magnetic sensor (flux valve) positioned in the wingtip”
is wrong.
The FMS
calculates magnetic heading and track from true heading and track, not from
position, so “The FMS calculates MH and MT from the FMC position” is
wrong.
Magnetic
variation is calculated by each IRS based on the respective IRS position and
the aircraft true heading, not magnetic heading, so “Magnetic variation is
calculated by each IRS based on the respective IRS position and the aircraft
magnetic heading” is wrong.
We are left
with only one option!