Cách sử dụng
The expression "sit up" means to move from a lying position to a sitting position. For example, if you are lying down on a bed or couch and someone asks you to sit up, they are telling you to lift your upper body and sit with your back straight. This expression can also be used to refer to a person's posture or attentiveness, as in "Please sit up straight" or "He didn't start paying attention until he sat up and listened."