Sure! Here are the answers to your questions:

**21. Mr Nam never turns up on time for a meeting.**
- The closest in meaning to "turns up" is:
**B. arrives**

**22. The Great Pyramid of Giza is one of the famous man-made wonders of the world.**
- The opposite in meaning to "man-made" is:
**A. natural**

**23. He hasn’t made (A) up their (B) mind where (C) to go on holiday (D) yet.**
- The mistake is in (B). "their" should be corrected to "his" or "her" (depending on the context) or to "his or her" if a gender-neutral option is preferred.
**Correction: He hasn't made up *his* mind where to go on holiday yet.**

**24. Mrs. Thom likes (A) making (B) the gardening in (C) her free time (D).**
- The mistake is in (C). The correct preposition should be "at" instead of "in."
**Correction: Mrs. Thom likes making the gardening *at* her free time.** (Alternatively, it may also be phrased as "likes gardening in her free time.")