When beginning the meeting, the fire alarm went off.

The fire alarm went

off when beginning the meeting.

OR

When we were beginning the meeting, the fire alarm went off.

'When we were beginning the meeting, the fire alarm went off.'

Explanation:

As per the question, the most appropriate revision or alternative to the given sentence would be 'When we were beginning the meeting, the fire alarm went off' as it correctly employs the use of past continuous tense in the subordinate clause and past indefinite (simple) tense in the principal clause together to elucidate the situation. In the given (original) sentence, the use of past continuous tense is inappropriate and the first option commits the same mistake. Therefore, the latter option is the correct one.