Let's fill in the blanks with the correct verb forms:

20. We lost the match. If you **had played** for us, we **would have won**.

Explanation: This is a third conditional sentence. "Had played" is the past perfect tense used in the if-clause, and "would have won" is the conditional perfect tense used in the main clause.

21. They would not be paid if they **did not do** their work well.

Explanation: This is a second conditional sentence. "Did not do" is the simple past tense used in the if-clause, and "would not be paid" is the conditional form used in the main clause.

22. If I became very rich, I **would build** a hospital for the poor.

Explanation: This is a second conditional sentence. "Became" is the simple past tense used in the if-clause, and "would build" is the conditional form used in the main clause.

These corrections ensure that each sentence uses the appropriate verb tense for expressing hypothetical situations in English.