I can help you identify and correct the mistakes in each of the sentences listed. Here are the corrections for each exercise:

1. In spite of her broken (C) **leg**, she tried to walk (D) **to** the school to attend (A) **the** lecture.
Correction: **leg** instead of broken.

2. Whenever (A) you will promise (B) to do something, you need (C) to keep (D) **your word**.
Correction: Remove **will** before promise.

3. No (A) matter how (B) expensive this car is, he decided (C) to buy (D) **it**.
Correction: Change **how** to **how much**.

4. Bob decided not to (A) set (B) that job (C) in spite of (D) **his** offer.
Correction: **his** instead of that.

5. There are (A) such (B) many things to do (C) that there is (D) **no time** to do them.
Correction: Change **things** to **an**.

6. Although (A) the traffic (B) was heavy, we managed (C) to get to (D) **the** meeting on time.
Correction: Change **to** before **the meeting**.

7. My sister is (A) too young (B) **to** volunteer (C) **for** the job.
Correction: Change **to** to **for**.

8. In spite of (B) my father has retired (C) I will finish (D) **this project**.
Correction: Change to **retiring**.

9. I hope she (A) still helps (B) to direct (C) the company (D) **the way you said** she would.
Correction: Remove **to** before **direct**.

10. I think John works (A) with (B) her, but (C) he is (D) **not**.
Correction: Change **is** to **isn't**.

11. Mary always behaves (A) childish (B) despite (C) the way she (D) **acts**.
Correction: Change **childish** to **childishly**.

12. Although (A) he couldn’t (B) get rid of (C) **smoking**, he decided (D) to stop.
Correction: Change **get rid of** to **stop**.

13. Because (A) he was (B) in his exam (C) **he failed** creatively (D) **also**.
Correction: Remove **also**.

14. He would rather (A) **continue** to write (B) the project, (C) as soon as (D) he will finish **it**.
Correction: Change **will** to **has**.

15. As soon as (A) she will finish (B) that project, (C) she will go (D) home with **her** husband.
Correction: Change **will** to **has**.

This should help you with the exercise! Let me know if you need further assistance.