Question

He --- (walk) across the bridge when his hat blew off

Answer 1

Answer:

Formation : was / were + the (-ing) form of the verb.

* Usage :        - an action which was going on during a certain time in the past.

- indicating that an action was going on at a time when another action took place.

  *Words used with the tense : all (yesterday) - while - as - when -  etc.

N.B.1_     WHILE and AS are followed by past continuous and the main verb in the past 

                 simple.

                 WHEN is followed by past simple and the main verb in the past continuous.

N.B.2_       Some verbs are not used in the continuous form.