La ortografía del participio presente

Completa las frases con la forma correcta del participio presente de los verbos entre paréntesis.
1. He is (write) a letter.
2. They are (sit) down.
3. She is (swim) in the lake.
4. It's (begin) to rain.
5. I'm (study) Chinese this year.
6. She's (lie) on the beach.
7. It's (get) dark sooner these days.
8. I'm (travel) to Lisbon this summer.
9. She's (cut) some bread.
10. I'm (see) the dentist next week.