Rewrite the following sentences

21.    It’s three years since I started using this bicycle.
    I have __________________________________________________________________
22.    No one has ever answered the questions.
    These questions __________________________________________________________
23.    I’ve arranged to meet Mr.Trung tomorrow evening.
    I’m ____________________________________________________________________
24.    “You’d better go to see the doctor immediately.”
    She advised _____________________________________________________________
25.    They want to buy a bigger house but they don’t have enough money.
    If they _________________________________________________________________