Teenagers should be allowed to make decisions for themselves.
该标题是should的被动语态；should+be+ done
Flowers should be watered every day.
还有考察allow的用法.
allow sb.to do sth.允许某人做某事
My mother allows me to watch TV.
sb.is allowed to do sth.某人被允许做某事
He is allowed to buy an iPhone 6.