The correct options are
A Construction of steam engine is complex.
B Steam engine is bulky, hence cannot be used to run small machines.
C The engine can't start instantly.
Due to its big boiler and furnace, a steam engine is huge, heavy and clumsy. Since the boiler of a steam engine is very heavy, therefore, a steam engine cannot be used for running small vehicles like cars and buses. Moreover, a steam engine does not start at once. Before a steam engine can start, we have to build a coal fire to get steam. This process takes a long time and hence a steam engine cannot be started instantly.