IV. Rewrite the sentence
1. Children have to live with their parents until they reach the age of 18. (obliged)
-> Children are obliged to live with their parents until they reach the age of 18. 
2. If I were you, I'd read the exam questions very carefully.
- You should read the exam questions very carefully. 
3. It's a good idea to swallow rapidly if you have hiccups.
-> You should swallow rapidly if you have hiccups. 
4. It is compulsory for girls to wear "ao dai" as an uniform.
-> Girls are required to wear "ao dai" as an uniform.