Step 1: State the concept.
A sustained release product is designed to slow down how quickly a drug becomes available, so that it dissolves and is absorbed gradually rather than all at once. The formulation must delay disintegration or dissolution.
Step 2: Think about what controls release speed.
Larger particle size means a smaller surface-area-to-volume ratio. Smaller surface area slows both disintegration and dissolution, which naturally stretches the release over a longer time.
Step 3: Evaluate the solid dispersion option.
Option 1 uses water soluble excipients in a solid dispersion, but that technique is meant to speed up dissolution of poorly soluble drugs, the opposite of sustaining release, so it is rejected.
Step 4: Evaluate the spray drying option.
Option 3 again pairs spray drying with water soluble excipients, which tends to produce fine, fast-dissolving particles, again the opposite of a sustained effect, so it is eliminated.
Step 5: Evaluate the disintegrant option.
Option 4, a good disintegrating agent, makes a dosage form break apart faster, giving immediate release, which directly contradicts the sustained release goal, so it is discarded.
Step 6: Conclude.
Only larger particles that delay disintegration genuinely slow the release, matching option 2 from the answer key.
\[ \boxed{\text{Option 2: Large particles delaying its disintegration}} \]