PAST SIMPLE OR PROGRESSIVE. ( раскрой скобки, верно употребив время) When

When I was walking to school I saw John.

We use Past Continuous in the first part of the sentence. Past Continuous is formed with the help of the past forms of the auxiliary verb to be. The past form of the auxiliary verb to be are was / were. Was is used for singular. Were is used for plural. We add the suffix ing to verb.

The second part of the sentence is in Past Indefinite. Past Indefinite is formed with the help of the suffix ed. We add ed when verb is regular. We use the second form of irregular verbs for Past Indefinite.

To see is an irregular verb. (to see saw).