1. you haven't visited Mum and Dad for weeks ( since )

--> It's weeks since you last visited Mum and Dad.

2 It wouldn't be a good idea to make him angry (better)
-->You had better not make him angry

3 That's the best meall . I've ever eaten (never)
-->I have never eaten such a good meal
4 We are meeting our friends at 9:00 (going)
-->We are going to meet our friends at 9:0 0
5 they won't pass the exam if they don't revise (unless)
-->they won't pass the exam unless they revise.

1, It's weeks since you last visited Mum and  Dad

2, You had better not make him angry

3, I have never eaten such a good meal 

4, We are going to meet our friends at 9:00

5, They won't pass the exam unless they revise

Study well