1-Unless John studies harder, he won't pass the final exams.
2-Not only does Sarah love to dance, but she also loves to sing.

1.If John doesn't study harder,he won't pass the final exam.=>Unless John studies harder, he won't pass the final exams.
2. Sarah both loves to dance and loves to sing.=>Not only does Sarah love to dance, but she also loves to sing.

1. Unless he studies harder, he won't pass the final exams
2. Not only Sarah loves to dance but also she loves to sing