Answer: D

Reasoning: Impression plaster sets into a highly rigid, brittle mass with virtually no elastic recovery; once hardened it cannot flex around undercuts, making disengagement from the tissues far more difficult than with elastic materials such as silicones or reversible hydrocolloids, and even more difficult than the slightly less rigid zinc-oxide/​eugenol pastes [Koffi 2005, PMID 16398307; Koran 1980, PMID 6987107].