Refer to figure.
There are two main types of drag:

• Parasite drag - which increases as airspeed increases. This consists of three different types of drag:
  • Form/profile drag: This is due to the shape of an object. It occurs due to the higher pressure upstream, and lower pressure downstream. It is worse for “blunt” bodies, like landing gear, and is reduced by reducing the frontal area.
  • Skin friction drag: This occurs due to the friction (viscosity) of air as it flows over the surfaces. It can be reduced by either reducing the surface area, or surface roughness.
  • Interference drag: This occurs due to the mixing of different airflows over a body. One stream may interfere with another, causing drag
• Induced drag - increases when the coefficient of lift is increased. This is usually the case when the angle of attack increases. In straight and level flight, induced drag increases as airspeed decreases.
  • Induced drag occurs due to the 3D flow characteristics around a wing. As the higher pressure air underneath the wing flows to the upper surface of the wing, it creates wingtip vortices. These vortices change the direction of airflow over the wing, tilting the lift vector backwards. The production of lift by the wings is what creates induced drag. 

the forward speed of the aeroplane. → INCORRECT. This is what leads to parasite drag, in all its forms.

the lift produced by the wings. → CORRECT.

the application of flaps. → INCORRECT. Induced drag exists with and without flaps. It is a result of wingtip vortices, which are a consequence of lift production. 

the shape of the aeroplane. → INCORRECT. This also refers to parasite drag, mainly form and interference drag. Although technically the shape of the aeroplane (that it has wings and lift producing surfaces) does lead to induced drag, but this is not the most correct answer option.