$1.$ I was standing right to her but she didn't recognize me.

$2.$ The road was slipping so they could't drive fast.

$3.$ If you works too fast perhaps that why you will make so many mistakes.

$4.$ People admire him because he has talent.

$5.$ Kien asked me to join his volunteer project and I agreed 

$6.$ Ba often get good grades because he always studies hard

$7.$ Be careful with the food you eat or you will have an allery

$8.$ Lan's mother was home late yesterday so she had to cook dinner herself

$9.$ To stay healthy, we should eat more vegetables and reduce high-fat food

$10.$ We talk and sing for the elderly people because it make them happy

1. I was standing right next to her. She didn’t recognize me. (but)

⇒ I was standing right next to her but he didn’t recognize me. 

2. They couldn’t drive fast. The road was slippery. (so)

⇒The road was slippery so they couldn’t drive fast. 

3. You work too fast. Perhaps that’s why you make so many mistakes.(if)

⇒If you work too fast , perhaps that’s why you make so many mistakes

4. People admire him. He has talent. (because)

⇒ People admire him because he has talent..

5. I agreed. Kien asked me to join his volunteer project. (and)

⇒Kien asked me to join his volunteer project and I agreed .

6.Ba often gets good grades. He always studies hard. ( Because )

⇒Ba often get good grades because he always studies hard.

7. You should be careful with the food you eat. You will have an allery. (Or )

⇒Be careful with the food you eat or you will have an allery.

8.She had to cook dinner herself. Lan’s mother was home late yesterday. (So)

⇒Lan's mother was home late yesterday so she had to cook dinner herself.

9.To stay healthy, we should eat more vegetables. We shouldreduce high-fat food. ( And )

⇒ To stay healthy, we should eat more vegetables and reduce high-fat food.

10. We talk and sing for the elderly people. It makes them happy (because)

⇒We talk and sing for the elderly people because it make them happy.