1) When I was young, my mom used to say hula hoop will make tummy smaller, is it true? and the body izzit can get S shape?
What i notice is true for those having fats at tummy but false for those having more 'meat' at tummy.

2) I have thick rough hair, how to make it thinner and smoother?
Buy hair shampoo, conditioner & serum from hair product shop but not supermarket. I used to use the one contains coconut smell. Hair become smoother. I think the only way to make your hair look thinner is "layer cut". No harm go and ask professional opinion.

3) I have big hips, what kind of exercise can make it smaller?
I would like to know too.

4) My teeth are yellow (Im a none smoker, and I brush my teeth everyday!well..maybe not when i was a kid but i am super regret now... ) and I am using colgate white for afew years now and still don't see any improvement. Is it possible to make it white?
Dentist may help you. By the way, i heard that it is advisable to change toothpaste brand every 1-3 years.