What is the precise chemical mechanism by which gypsum (CaSO4.2H2O) retards the setting of Portland cement?

Options:

• A: It reacts with tricalcium silicate (C3S) to form a protective layer of calcium silicate hydrate gel, slowing down water absorption.
• B: It reacts with tricalcium aluminate (C3A) to form insoluble crystals of ettringite (calcium sulfoaluminate) on the surface of aluminate particles, temporarily barrier-coating them.
• C: It increases the solubility of dicalcium silicate (C2S), allowing it to hydrate faster than tricalcium aluminate.
• D: It acts as a catalyst that accelerates the evaporation of excess water, preventing premature crystallization.

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