1. Once you decide, you can't change your mind.
2. Once you have a stomachache, take the medicine twice a day.
3. Once he finds out what you've done, he'll get mad.
A: My friends have been asking me to smoke cigarettes with them.
B: Be careful! You don't give in to peer pressure.
B: First of all ,smoking is bad for your health and second, once you start smoking it will be hard to stop.
A: Yeah, you're right. I know a lot of people who are addicted to smoking.
B: I bet most of them started because their friends also smoked.
A: You're right. I won't do it. I won't smoke with my friends.