用动词的适当时态填空。
1. —Oh, what a beautiful song!
—Who ________ this song? (sing)
2. —Where ________we________ (meet)?
—Let's meet outside the park gate.
3.—Where is Tom?
—He ________ (go) to the post office. I think he ________ (come) back soon.
4.Your brother _________ ( study) it since he was ten years old.
5.How long ________ you _________ (do) your homework so far?