A diesel engine with a combustion chamber located between the crowns of two pistons is known as a/an __________.

Correct Answer: Option B — opposed-piston engine

An opposed-piston engine utilizes two pistons reciprocating within a single cylinder bore in opposite directions. The combustion chamber is formed between their crowns at top dead center, eliminating cylinder heads and enabling efficient scavenging and high power-to-weight ratios typical of large two-stroke marine propulsion plants.