Sure! Here are the sentences completed with the appropriate articles and explanations:

1. Your soup is so good. **The** meat is pretty tender.
- "The" is used here because contextually we are referring to a specific meat that is part of the soup.

2. Are you interested in **science** or **music**?
- No article is needed here because both "science" and "music" are uncountable nouns when referring to the fields in general.

3. They got married but **their** marriage wasn’t very successful.
- "Their" indicates possession and refers to the marriage of the couple.

4. Do you know any of **the** people who live across **the** road?
- "The" is used before "people" because it refers to specific people known in the context. "The" before "road" specifies which road is being talked about.

5. After **work** the boss usually invites his staff to **the** pub.
- "Work" is uncountable in this context and doesn’t need an article. "The" indicates a specific pub known to the speaker.

6. When mom was ill **a** lot of her friends came to **the** hospital to visit her.
- "A lot" is used as a phrase meaning many, and "the" specifies which hospital.

7. Many people hate **violence**, but they like to watch it in **movies**.
- No article is used for both "violence" (uncountable in this context) and "movies" (plural and general).

8. Have you ever visited **Madame Tussaud’s** in London?
- No article is needed since "Madame Tussaud’s" is a proper noun referring to a specific place.

9. **Life** would be difficult without **the** useful machines and gadgets we have today.
- "Life" is referred to in a general sense, while "the" points to specific machines and gadgets.

10. I’m on **night** duty this week.
- "Night duty" is a specific phrase and doesn’t need an article here.

11. I know someone who wrote **a** book about **the** American presidents.
- "A" indicates any singular book, while "the" specifies the group of presidents.

12. **World War II** ended in 1945.
- No article is needed because "World War II" is a proper noun.

13. **The** fumes of cars and factories are **the** primary reasons for **air** pollution.
- "The" is used to specify particular fumes and the specific reasons.

14. He was **an** unsuccessful musician when he came to this town.
- "An" is used here because "unsuccessful musician" begins with a vowel sound.

15. Don’t stay in that hotel. **The** beds there are very uncomfortable.
- "The" is used to specify the particular beds in that hotel.

16. The car sped away at **a** hundred km **per** hour.
- "A" is used before "hundred" to indicate an unspecified number of hundreds; "per" is a standard expression for rates.

17. John doesn’t usually go to **church** on **Sundays**.
- "Church" doesn’t need an article when referring to the institution in general; "Sundays" is a plural noun that typically doesn’t use an article.

18. He was sent to **prison** for **murder**.
- "Prison" doesn’t need an article when referring to the institution in general; "murder" also doesn't require one in this context.

19. At **the** beginning of his speech he spoke about **tourism** in general.
- "The" is used for specifying a particular beginning, while "tourism" is uncountable here.

20. We usually go by **train**, but today we’re taking **a** bus.
- "Train" when referring to modes of transportation does not need an article; "a" is used before "bus" because it refers to one of many buses.

Feel free to ask if you need further clarification on any of these points!