Xv. open brackets using passive or active voice. 1. he said that grandmother’s letter (to receive) the day before. 2. two new engineers just (to introduce) to the head of the department. 3. we (to finish) this work in time. 4. they (to build) this house in 2001. 5. they (to sell) new children’s books at that shop when i entered it yesterday.

1had been received
2has been just introduced
3will finish
4built
5were selling

1. He said that grandmother's letter had been received the day before.

In this sentence, we use the passive voice because the focus is on the action of receiving the letter rather than who received it. The verb "to be" is used in its past tense form "had been" and the past participle form of the verb "receive" is used, which is "received".

2. Two new engineers have just been introduced to the head of the department.

Again, the passive voice is used here because the focus is on the action of introducing the engineers to the head of the department. The verb "to be" is used in its present tense form "have been" and the past participle form of the verb "introduce" is used, which is "introduced".

3. This work will be finished by us in time.

For this sentence, we use the passive voice to show that the work will be completed by us. The verb "to be" is used in its future tense form "will be" and the base form of the verb "finish" is used, which is "finish".

4. This house was built in 2001.

In this sentence, the passive voice is used to focus on the action of building the house. The verb "to be" is used in its past tense form "was" and the past participle form of the verb "build" is used, which is "built".

5. New children's books were being sold at that shop when I entered it yesterday.

Here, the passive voice is used to show the action of selling the books. The verb "to be" is used in its past tense form "were being" and the present participle form of the verb "sell" is used, which is "selling". Additionally, the word "when" is used to indicate the time when the action took place.

I hope this explanation helps you understand the usage of passive and active voice in these sentences. If you have any further questions, feel free to ask!