Select the most appropriate option to fill in the blank.
Despite initial problems, the plan has been a ______ success.

Correct option is D

The correct option to fill in the blank is (d) roaring.
"Roaring success" is a common idiomatic phrase meaning tremendous or resounding success. (शानदार सफलता)
Example: The movie was a roaring success at the box office.
Explain why other options are incorrect:
· (a) loud: high volume sound (तेज़ आवाज़), not contextually suitable.
· (b) sounding: incomplete and awkward usage.
· (c) cracking: informal, but not standard usage with “success”.