a). A slight leak on the cylinder head gasket causes the cooling system pressure to leak coolant into the cylinders after the engine is switched off. A minimal amount of coolant is leaked and upon starting, the coolant is expelled through the exhaust as the engine is started.
Sometimes you can jut put your hand over the tailpipe and let it pump pressure against your hand quickly pull it away and smell it to see if it smells like anti-freeze.
It is a simply test you may be able to detect a leak into the cylinder.