Irregular and regular verbs

Match it! Select the correct answer from the pull down...Good luck!

They ______ (forget) their passwords

You ______ (find) the book under the bed.

I _______ (not buy) a new house, I ______ (buy) a new car.

I _______ (feed) all the dogs

I think he _____ (catch) a cold.

Choose the form of the verb in brackets: I ______ (see) her crying in the garden sometimes.

We _____ (know) the answer.

What is the simple past form of the verbs UNDERSTAND-FORGET-BELIEVE?