1. She has beautiful short wavy brown hair.
2. I've been drinking four cups of coffee for an hour.
=> it means, you've been taking sips from four different cups of coffee for the past hour.
3. What do you think it will happen?
=> 'What' is the subject of the verb 'will happen'. There should be only one subject per verb:
You think what will happen?
What will happen do you think?
What do you think will happen?
Hopes that helps.