Не понимаю упражнение по английскому языку. Помогите сделать, буду благодарна!

2.Please send us another copy of our invoice and we will pay it at once.
If you send us another copy of our invoice, we will pay it at once.
We will pay it at once if you send us another copy of our invoice.

3.The consignment was packed for export and loaded on to the truck.
Before being loaded on to the truck, the consignment was packed for export.
Before the consignment was loaded on to the truck, it had been packed for export.
The consignment had been packed for export before it was loaded on to the truck.

4.Each order is manufactured and the packaging is printed at the same time.
The packaging is printed while an order is manufactured.

5.Your letter was delayed in the post and we have not been able to process your order yet.
We have not been able to process your order because your letter was delayed in the post.
Because your letter was delayed in the post, we have not been able to process your order.

6.Please inform us of your telex number and we will be able to reply to your query at once.
Please inform us of your telex number so that we can reply to your query at once.

Написано: Discuss the punctuation with the teacher- Обсудите пунктуации с учителем, всё
иди к учителю :D, это вся суть задания. сделай это с учителем.

Какой класс?