Here are the present tense forms for the sentences:

1. Listen! I (think) **am thinking** someone (knock) **is knocking** at the door.
2. Up to the present, we (write) **have written** almost every lesson in the book.
3. The earth (circle) **circles** the sun once every 365 days.
4. The farmer (work) **is working** in the field at the moment.
5. Rivers usually (flow) **flow** to the sea.
6. How many times (see) **have you seen** him since he went to London?
7. I (wait) **have waited** for the manager for two hours.
8. Mrs. Green always (go) **goes** to work by bus.
9. Look! The boy (cry) **is crying**.
10. You (ever, see) **have you ever seen** a monkey?

Feel free to ask for more help if needed!