What happens to make electrical current flow in a generator?

Generators don’t actually create electricity. Instead, they convert mechanical or chemical energy into electrical energy. They do this by capturing the power of motion and turning it into electrical energy by forcing electrons from the external source through an electrical circuit. A generator is essentially an electrical motor working in reverse.
Some electrical generators, such as those at Hoover Dam, for example, are huge and provide enormous amounts of energy by transferring the power created by water turning turbines into electricity. Residential and commercial generators, however, are much smaller and rely on more traditional fuel sources like diesel, gas, and propane to create mechanical power that can then be forced into a circuit and induce an electrical current.
Once an electrical current has been established, it is directed through copper wires to power external machines, devices, or entire electrical systems.

Ithink the answer would be a 

The upward force acting on the wing of a airplane in flight is known as the "lift" force. (d)