23.
(A) about those
(B) about which
(C) for it
(D) for which

Full Sentence:

Intrinsically motivated activities are ones for which there is no apparent reward except the activity itself.內在動機活動是指除了活動本身之外沒有明顯獎勵的活動。

Explanation:

• The phrase "for which" is a relative pronoun construction that correctly links "activities" to the clause "there is no apparent reward."

• You're essentially saying: "There is no apparent reward for these activities — except the activity itself."

• activity 前面的介系詞搭配 for, 你不會說 about the activity

Why the others are incorrect:

• (A) about those – Grammatically awkward and incorrect; doesn't link the clauses properly. -- 介系詞搭不上，接指示代名詞 those 也很奇怪

• (B) about which– Incorrect preposition; the activity isn't "about" the reward. -- activity 前面的介系詞搭配 for, 你不會說 about the activity

• (C) for it – Refers to a singular object and doesn't properly link the relative clause to "activities." --it 是單數，和後面的 activities 的複數型態搭不上

✅ Correct form: "for which" = the appropriate relative pronoun + preposition structure.