Step 1: Analyse the Assertion.
Predators generally do not eliminate all prey organisms.
This helps maintain ecological balance.
Hence Assertion is true.
Step 2: Analyse the Reason.
If prey disappears completely, predators lose their food source.
This may result in extinction of predators.
Hence Reason is true.
Step 3: Check the explanation.
The reason explains why predators are prudent in food utilization.
Therefore,
\[
\boxed{\text{Option (A)}}
\]
is correct.