Pin down the two humidity terms first, since their definitions are short and specific. Absolute humidity is just water vapour mass per unit mass of dry air, which is the ratio of kg of water vapour in kg of dry air; percent humidity compares that ratio to the saturation value at the same temperature, which is the ratio of humidity with respect to humidity at saturation point. That leaves the two drying periods to match with the two moisture terms. The constant rate period runs while free surface moisture is available and ends exactly at the critical moisture content, so Constant rate period pairs with Critical moisture content. The falling rate period is the tail end of drying where the rate keeps falling until the material settles at its equilibrium moisture content, so Falling rate period pairs with Equilibrium moisture content. \[\boxed{(A)-(III),\ (B)-(IV),\ (C)-(I),\ (D)-(II)}\]