The steam engine was invented by
A. James Watt
B. Joule
C. Newcomen
D. Newton

Hint: Steam engine is a type of heat engine that is used to perform mechanical work using steam. Just like all devices it was invented by a scientist and then improved by others in future. Among the given options of scientists we have to choose the one who performed the functions that resulted in the initial formation of a steam engine.

Complete answer:
Steam engine is a machine that revolutionised a century and led to the industrial revolution. The basic working of a steam engine is that it uses the forces which are produced due to the steam pressure and then pushes a piston back and forth inside a cylindrical vessel thus performing mechanical work. Then the force pushing the piston is transformed into rotational force for work by using a connecting rod and a flywheel.
The first steam engine machine which was a commercially used engine was invented by Thomas Newcomen in 1712. Later in 1765 James watt improved the working of this basic structure of steam engine greatly by making very crucial improvements in the design. This was achieved by removing the spent steam to separate vessels for condensation of the steam, this in turn resulted in a vast improvement of the amount of work obtained per unit fuel consumed.

Therefore, the correct option for the question is C, Newcomen.

Note:
In order to have high efficiency of a steam engine, its steam must go through a wide range of temperatures because due to this it would result in higher expansion of the steam within the engine.