The correct answer is A) Research Department Explosive. RDX is a powerful explosive widely used in military and industrial applications. The acronym originated from the British Research Department in the 1930s. RDX is also known by other names such as cyclonite or hexogen. It is a key component in various explosive mixtures, including C-4 plastic explosive. While the name RDX is commonly cited as originating from “Research Department Explosive” in the UK, it is sometimes also said to stand for “Royal Demolition Explosive”. The UK origin is the most widely accepted for the acronym itself.