Asteam boat is an example of a machine that uses a( combustion engine.
a) internal
b) external

The correct answer is external combustion engine.

Explanation:

External combustion engine is an engine in which working fluid is present inside and heated up by the combustion by the source present out the engine.

In a steam boat, fuel is burnt to heat up the water present in the boiler. during boiling of water, water vapor expand and pushes the base of piston. During this push heat energy is converting into mechanical energy which pushes the boat in the forward direction.

Internal combustion engine is an engine in which burning of the fuel takes place inside the engine and heat derived from the combustion then used to perform mechanical work