Explanation

@madelyn-luskey (A) is incorrect because Clay's argument only ever refers to "life as we know it." Therefore, any claim about "forms of life OTHER than life as we know it" would not weaken (or strengthen for that matter) Clay's argument. (C) is correct because it weakens Clay's argument. Clay's argument relies on the necessary assumption that the instruments currently available can detect planets outside our solar system. If that was NOT the case, then the premise that "astronomers to date have not detected even one planet outside our solar system" would simply be a description of the current limitations of astronomical instruments. We would not be able to make any further conclusions from that premise. Therefore, if Clay accepted that "Detecting planets outside our solar system requires more sophisticated instruments than are currently available," the necessary assumption would not be met, and Clay would have to reconsider his conclusion. I hope that helps! Let us know if you have any more questions.

thanks

@Victorvtg, let us know if you have any more questions—we're here to help!