Answer choices C and E

Hi @shafieiava, You are correct that it is tricky to identify sufficient/necessary language in the stimulus, I in fact didn't notice it until I read (D). Answer (D) is correct though because it accurately identifies the flaw in the logic. The expert tells us that researchers have shown that an antenna must be symmetrical and have fractal structure to work equally well at all frequencies. Then, the expert tells us that this is incorrect because an antenna with both qualities doesn't work equally well at all frequencies. This expert is forgetting that maybe there are other requirements beyond fractal structure and symmetry that may need to be true for the antenna to work equally well at all frequencies. Aka, the expert is claiming that fractal structure/symmetry are sufficient for an antenna to work equally well at all frequencies, when really all we know is that they are necessary. (C) is incorrect because it misunderstands the logic being used. This argument is not about a lack of evidence that something is true, but rather the expert is confusing what is a necessary versus sufficient condition. The expert does not claim there is insufficient evidence to support something being true- instead he just points to a backwards logic to determine something is false. (E) is incorrect because it is irrelevant. Say there was a third possibility (aka right at 250), the evidence provided would still show that the antenna is not working the same at all frequencies. This doesn't really get to the main thrust of the expert's argument.

@Annie this was very helpful! Thank you.

@shafieiava, let us know if you have any other questions!