Explanation
Correct answer: A.
Choice A is the best answer because it most accurately describes how the underlined phrase functions in the text as a whole. The text states that the wax produced by Liu and colleagues’ reactor can be turned into a surfactant. The underlined phrase, which is set off with parentheses, then provides a definition for the term "surfactant," explaining that it’s a chemical compound that can be used as a detergent. Thus, the underlined portion of the text functions to clarify the meaning of a scientific term.
Why the other choices are wrong
Choice B
Choice B is incorrect. Though the text as a whole focuses broadly on an environmental concern, the underlined phrase does not; it simply indicates what a surfactant is.
Choice C
Choice C is incorrect. Though the text as a whole focuses on a scientific discovery (Liu and colleagues’ solution to the problem of plastic recycling), the underlined phrase does not explain its significance; it simply defines a scientific term used in the discussion.
Choice D
Choice D is incorrect. Though the text as a whole includes discussion of the result found by Liu and colleagues, the underlined phrase does not discuss it; it simply defines a scientific term used in the discussion. Additionally, at no point in the text is it mentioned that the team was confused.