‘All at once’ means -

A suddenly

B quickly

C slowly

D gradually

Correct Answer: Option A

All at once (হঠাৎ) idiom-টির অর্থ- suddenly (হঠাৎ/আকস্মাৎ)।

Quickly- দ্রুত;
slowly- ধীরে;
gradually- ক্রমান্বয়ে।