Why is A correct?

@Shiyi-Zhang, Happy to help. Let's take a look at (A) and (E). (E) says, "Prior to their discussions with the researchers, the family members did not describe their occasional use of Spanish as serving to emphasize humor or intimacy" (E) is consistent with the author's take on the study in the passage. The author states that "often the switches [for rhetorical effect] are so subtle that the speakers themselves are not aware of them" (lines 49-50). This provides support for the assertion that the family members would not coin their sporadic usage of Spanish as something that emphasizes intimacy and humor until some researchers noted that they sometimes used Spanish. Thus, (E) does not cast doubt on the author's point, so we can get rid of this answer choice. (A) says, "In a previous twelve-month study involving the same family in their home, their conversations were entirely in English except when situational factors changed significantly." We're looking to weaken the author's analysis of the study involving the family's code-switching for rhetorical effect. The author concludes from the study that certain instances of code-switching can't be fully explained by situational factors because rhetorical factors (such as the desire to show humor or intimacy) caused the family to sometimes use Spanish (lines 51-59). There are a number of ways in which causal statements can be weakened. One method is to give an example of the effect without its purported cause, and this is exactly what (A) provides us. (A) says that for a whole year, the family spoke in Spanish only when situational factors changed a lot. This weakens the author's conclusion because it shows the use of Spanish without the presence of the purported cause (rhetorical factors), so (A) is the correct answer choice. Does this make sense? Let us know if you have any more questions!

Why is C incorrect? I still don't get this question after reading the answer. Could you please elaborate? Thanks

Is C incorrect because of the term "occasionally"? Thank you for all of your help!