Ответ:

1. Colin wouldn't have met Dawn, if a friend hadn't invited them to a party.

2. Dawn would have been happy, if she had changed her hairstyle.

3. Spike wouldn't have wanted a tattoo, if his friend hadn't had one.

4. Spike wouldn't have ask her out Stella if she hadn't been liked by him.

5. Stella would have gone out with Spike if she had liked his hair