“Recent”

Hello @DavidW, I'm not crazy about the use of "recent" in answer choice A either, but it is a small problem compared to the flaws in the other answer choices. Sometimes, we do have to be flexible with word choice on reading comp questions. They will use a lot of rough synonyms in the answer choices that don't perfectly match the passage. We have to accept this at times when it doesn't seriously change the meaning. I do see some support for A on line 20, which suggests that these secondary substances "continue to appear" as a result of genetic mutation. This is enough for us to reasonably accept the word "recent" in answer choice A.