Past Simple affirmative & negative sentences

We really (a)   (enjoy) the game last Sunday.

They (a)   (not play) very well yesterday. They lost the match.

Sandra (a)   (not want) to go rowing with me.

I (a)   (buy) a new baseball cap last week.

James (a)   (stop) his car in front of the sports shops.

I (a)   (do) my maths homework yesterday.

They (a)   (visit) a farm two weeks ago.

Jenny and Peggy (a)   (not, help) their brother.

He (a)   (not, drink) milk at school.

What's the past simple form of UNDERSTAND?

(a)