Answer:
1. The storm destroyed the sandcastle that we (build) had built.
2. He (not / be<u>)had not been</u> to Cape Town before 1997.
3. When she went out to play, she (do / already) <u>had already done</u> her homework.
4. My brother ate all of the cake that our mum (make) <u>had made</u>.
5. The doctor took off the plaster that he (put on) <u>had put on </u>six weeks before.
6. The waiter brought a drink that I (not / order) <u>had not ordered</u>.
7. I could not remember the poem we (learn) <u>had learned </u>the week before.
8. The children collected the chestnuts that (fall) <u>had fallen</u> from the tree.
9. (he / phone)<u>Had he phoned </u>Angie before he went to see her in London?
10. She (not / ride) <u>had not ridden</u> a horse before that day
Explanation:
The tense that we have to use to fill the blanks is past perfect simple. We use this tense when we want to talk about an action that took place before another event in the past. Usually, the other situation is in the past simple.
The structure of the past perfect is: the subject (he, she, it, we, you, they, you, I) followed by the auxiliary had and the verb in the past participle.
For example, in the sentence, John <u>knew</u> the town because he had visited it in the past. Knew, is the past simple of know while had visited, is the part of the sentence that is in past perfect simple, and we can see that is referring to an event in the past (knew the city) because of the action that he made previously to that (had visited it in the past).