Answer:
1. There are lots of parties <em><u>at</u></em> Christmas.
2. I received a letter <em><u>from</u></em> my friend yesterday.
3. She usually goes swimming <em><u>on</u></em> Sunday mornings.
4. Khoi is my close friend. I spend most of my free time <em><u>with</u></em> him.
5. He does volunteer work <em><u>at</u></em> a local hospital.
6. His friends didn't laugh <em><u>at</u></em> his jokes.
7. My friends usually enjoy my sense <em><u>of</u></em> humor.
8. He lives <u><em>at</em></u> 26 Tran Phu Street Ha Noi.
Explanation:
Prepositions are the words that tell us the position, place, or time of a thing. In other words, prepositions show us the relation of one thing to another.
In the given sentences, the respective prepositions are given as below-
1. There are lots of parties <em><u>at</u></em> Christmas.
2. I received a letter <em><u>from</u></em> my friend yesterday.
3. She usually goes swimming <em><u>on</u></em> Sunday mornings.
4. Khoi is my close friend. I spend most of my free time <em><u>with</u></em> him.
5. He does volunteer work <em><u>at</u></em> a local hospital.
6. His friends didn't laugh <em><u>at</u></em> his jokes.
7. My friends usually enjoy my sense <em><u>of</u></em> humor.
8. He lives <u><em>at</em></u> 26 Tran Phu Street Ha Noi.