1.According to the rules,it's necessary for students to hand in their assignments on time
-Students must hand in their assignments on time according to the rules.

Hoa wants to study overseas,but he is afraid of living alone
>Although Hoa wants to study overseas, he is afraid of living alone.

She doesn't get the first prize in the English Club.She is happy with the result
>Although she didn't get the first prize in the English Club, she is happy with the result.

jenny got up late,so she didn't get to school on timeJenny didn't get to school on time 
>because she got up late.

It isn't necessary for Cathy to buy new textbooks because she can borrow them from the library
>Cathy doesn't need to buy new textbooks because she can borrow them from the library.