In the normal course of evolution and adaptation, what is the most likely way for wings to develop in a tetrapod (four-limbed organism)?

a major mutation will produce new limbs, called wings, with a skeletal structure suited to flight. if this does not happen, flight cannot be achieved.

the forelimbs (or possibly hind limbs) will be used for the new purpose of flight. this new function will arise through many gradual steps, and there will be aspects of the wing that reflect its history and are not perfectly suited for flight.

a new, third pair of limbs will form. unlike the other four limbs, these wings will have a lightweight skeletal structure that is designed "from scratch" and is perfectly suited for supporting flight.

the forelimbs (or hind limbs) will be used for the new purpose of flight. natural selection will totally rearrange the elements of the skeleton to perfect the limb for its new function as a wing.

The correct option is this: The forelimbs (or possibly hind limbs) will be used for the new purpose of flight. This new function will arise through many gradual steps, and there will be aspects of the wing that reflect its history and are not perfectly suited for flight.  

Adaptation refers to the physical or behavioral traits that an organism develop in order to enhance its suitability to its environment. Evolution on the other hand is always brought about by natural selection; organisms that are well adapted to their environments are naturally selected to survive, reproduce and pass their beneficial traits to their offspring. This is a gradual process that occurs over a long period of time.  

For wings to develop in a four limbed organism, the organism has to start using the hind or the fore limbs for flight (New adaptive behavior). The genes that support this new behavior will be passed to its offspring and subsequent generations over a long period of time, until the wings are perfectly suited for flight.