At every scheduling decision, calculate the distance from the current head position to each pending request.
If the current head is at cylinder $50$ and requests are $:20,\ 47,\ 65,\ 90$
the distances are $:30,\ 3,\ 15,\ 40$
So SSTF chooses cylinder $47$.
The algorithm therefore makes a local greedy choice:
$\boxed{\mathrm{Choose\ the\ nearest\ pending\ cylinder}}$
Hence,
Answer : $\boxed{\mathrm{C}}$
