Answer:
1. The young man <em><u>ought not to drive</u></em> so fast through the town.
2. We <u><em>needn't have left</em></u> our house during the heavy rain because it didn't flood.
3. The police think the victim <em><u>might have known</u></em> the burglar.
4. You <em><u>mustn't be in</u></em> this building because it is unsafe after the earthquake.
5. <u><em>Shall we</em></u> buy this new eco-friendly product?
6. How do you <em><u>put up with</u></em> her bad behavior?
7. By 2050, the number of people on the planet <em><u>would have reached</u></em> about 9 million.
Explanation:
The use of the given words in bold require the addition of certain other words to make the whole statement correct. This means that aside from the given words, other words or phrases are also to be added according to their requirements.
The correct sentences after using the words in bold are as below-
1. The young man <em><u>ought not to drive</u></em> so fast through the town.
2. We <u><em>needn't have left</em></u> our house during the heavy rain because it didn't flood.
3. The police think the victim <em><u>might have known</u></em> the burglar.
4. You <em><u>mustn't be in</u></em> this building because it is unsafe after the earthquake.
5. <u><em>Shall we</em></u> buy this new eco-friendly product?
6. How do you <em><u>put up with</u></em> her bad behavior?
7. By 2050, the number of people on the planet <em><u>would have reached</u></em> about 9 million.