Refer to figure. 
Propellers generate 4 main secondary effects on an aircraft:

• Torque effect
• Gyroscopic precession
• Slipstream
• Asymmetric blade effect

For this question, we can go through each statement and check whether the effect is correct or not for the scenario, keeping in mind we are asked about a high power wartime era aircraft.

TORQUE EFFECT 
The anti-clockwise rotating propeller gains more anti-clockwise rotational momentum when the pilot adds thrust (higher RPM), so the aircraft experiences the opposite (clockwise) rotation, and is rolled to the right (this can be corrected using left aileron). On the ground, the additional force makes the aircraft “heavier” on the right wheel and the increased friction on this side yaws the aircraft to the right. The torque effect can be exacerbated by engines with high power as these produce higher torque.

GYROSCOPIC PRECESSION 
The propeller is a mass, spinning at high speed, and therefore acts as a gyroscope. That means that any rotation of the aircraft in pitch or yaw will gain a different force from the propeller due to gyroscopic precession. The force from the propeller will be rotated by 90º in the direction of rotation. In this case, the pitch-up will cause an forward force on the bottom of the propeller disc, which is rotated by precession to a forwards force on the right of the propeller disc. This creates a yaw to the left.

SLIPSTREAM EFFECT 
The spinning of the propeller affects the air that it pushes backwards, and imparts a spiral onto that air, in this case spiralling anti-clockwise around the aircraft, hitting the tail fin on the right hand side, causing a tail-left, nose-right moment. The slipstream increases with an increase in thrust, causing a yaw to the right.

ASYMMETRIC BLADE EFFECT 
The asymmetric blade effect comes from the aircraft being at an angle of attack to the air, so the air does not flow perpendicular to the propeller disc. The down-going propeller blades always produce more thrust than the up-going blades, so the thrust line of this anti-clockwise propeller is to the left of centre. An increase in thrust will therefore cause a larger force through this location (left of centre), which yaws the aircraft to the right.

Note: Asymmetric blade effect (P-factor) comes into effect after rotation when the propeller is inclined relative to the oncoming air. Gyroscopic effects only occur when the aircraft is rotated at takeoff. One could argue that slipstream effect could also be an option. However, according to feedback, “torque effect” was the correct answer.