This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to copy a key
Hold the teeth on one side of the key over an open flame until they are charred.
Use a lighter or a lit candle. Move the teeth of the key back and forth over the flame.

Possible answers:
[a]. Hold them until there is no burning, then keep holding them. You now have one duplicate key that is blue, white, or orange.;
[b]. You want the teeth to smoke on the flame, never burn them. Do not allow the flame to touch a lighter.;
[c]. It should take around 1 or 2 minutes to blacken one side of the key. Once the key is charred on one side, set it down until it is cool to the touch.;
[d]. The material inside will help break down the wax in that area, which helps to reduce the likelihood of reconversion. Turn off the flame, then perform the copying at the same time.;
The answer is:
[c].