想請問一下這題文法題
20. Ecologists often study issues ____ the effects of human activities upon
populations and ecosystems.
(A) whom relate to
(B) which relates to
(C) that relate to
(D) that they relate to
請問D選項 為何不能解釋成名詞子句，they= issues這樣
明明知道很怪但說不出論點，還請各位賜教，非常感謝!

they (ecologists) relate the issues to the effects...

所以請問文法上是錯在they不能指定是issues這樣嗎?

if you insist "that" 就是issues, then it should be ~that are related to the effects... 先試著理解relate 這個字的用法。勿跟 the way that... the reason that...混談它們2者慣用法不像這句有想被關聯的先行詞

好的~謝謝指導，當名詞子句來看語意也不大通我覺得