"cylinder" is to "lock" as "engine" is to

a car

Explanation:

To understand this, we have to understand how important the cylinder is to a lock. The pin tumbler, the lock mechanism that makes a lock open with a key and not with another, is commonly used in cylinder locks. When that is the kind of lock, an outer casing will have a cylindrical hole. In that hole is where the plug is placed. And, in order to open the lock, this plug must be rotated.

So the Cylinder is pretty much the whole thing that makes the lock work. Inside of it, are the mechanisms and important things that make the lock work as it is supposed to. In the same way, without the engine, a car doesn't work.

a and b are the correct answer to what your looking fior

i don't know and i don't care .