Here are the corrections for the sentences provided:

1. Mommy, someone **is** calling me from an unknown number. I won’t answer it. (A: someone **is**)
2. My alarm rings at 6 o’clock every morning. Therefore, I always **go** to school on time. (B: went **go**)
3. We can’t play golf. It **is raining** hard outside. (C: rains **is raining**)
4. Ms. Lien is so kind that she **donates** thousands of pounds to charity twice yearly. (D: is donating **donates**)
5. Acupuncture is one of the oldest medical **treatments** in the world. (A: treatment **treatments**)
6. Many fatal accidents **are** caused by careless driving. (B: is **are**)
7. The practice of acupuncture is rooted in the idea of promoting harmony among humans and the world around them. (No correction needed)
8. Lan studied hard for the final test, but she **didn’t pass** with flying colours. (B: passed **didn’t pass**)
9. She’s counting her calories, so she really doesn’t want to eat dessert after meals. (D: wants **doesn’t want**)
10. Dogs are loyal pets, for they will never make you **feel** betrayed. (D: feeling **feel**)
11. We went to the Korean restaurant, but we found out it was closed early. (B: so **but**)
12. Don’t forget your passport, or you’ll have trouble checking in. (A: and **or**)
13. The lives of disadvantaged students are often very different **from** those of their more wealthy peers. (A: for **from**)
14. There are lots of **amusing** ways to volunteer in the arts such as teaching, designing and assisting with a variety of arts and crafts. (A: amused **amusing**)
15. Mahatma Gandhi fought for the rights of poor people and women in India and became a hero for millions of people. (B: against **for**)
16. While he and his **wife** Ali first went to Africa, they worked in a refugee camp for a month. (C: wile **wife**)
17. He worked in a big bank in London when suddenly he decided to leave **the** city to take part in Volunteer Bolivia. (B: this **the**)
18. IBM is an artificial intelligence computer system and is used to **answer** questions posed in natural language. (D: answering **answer**)
19. Vaccination has been used for a long time to **prevent** diseases. (A: for **to**)
20. After a two-hour discussion, we decided **to expand** the car market in America the following month. (D: expanding **to expand**)

Feel free to ask if you need further clarification on any of the corrections!