act on／upon
1．exert influence on产生影响
The medicine acted on his fever at once．这种药很快使他退烧了。
2．follow；behave according to遵照（行事）
She acted on the doctor's advice．她遵医嘱行事。
You should act upon this letter at once，or it will be too late．你应该马上按这封信的意思去做，不然就会太晚了。