Step 1: Compare wet and dry milling of pulses.
Wet milling involves soaking or steeping the pulse in water before dehusking and splitting, while dry milling uses little or no soaking. The Assertion states that dahl from wet milling takes longer to cook than dahl from dry milling, which matches known milling behaviour since prolonged soaking changes the grain structure.
Step 2: Examine the Reason on its own.
Longer steeping time allows more water to penetrate the seed coat and alter the starch and protein matrix inside, and it is well documented that dhal subjected to longer steeping tends to need more cooking time afterward, so the Reason is also true taken by itself.
Step 3: Link cause to effect.
Since wet milling by definition includes a longer steeping stage than dry milling, the longer steeping time is precisely why wet milled dahl needs more time to cook, so the Reason directly and correctly explains the Assertion.
\[ \boxed{Both (A) and (R) are true and (R) is the correct explanation of (A).} \]