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。