Explanation
Correct answer: B.
Choice B is the best answer. “In contrast” logically signals that the information in this sentence—that ABA triggers accelerated growth in the mustard plant Schrenkiella parvula—contrasts with the previous information about ABA triggering a slowdown in most plants’ biological processes.
Why the other choices are wrong
Choice A
Choice A is incorrect because “moreover” illogically signals that the information in this sentence about the mustard plant merely adds to the previous information about the effects of ABA. Instead, it contrasts with that information.
Choice C
Choice C is incorrect because “for example” illogically signals that the information in this sentence about the mustard plant provides an example consistent with the previous information about the effects of ABA. Instead, it contrasts with that information.
Choice D
Choice D is incorrect because “thus” illogically signals that the information in this sentence about the mustard plant is a consequence, or result, of the previous information about the effects of ABA. Instead, it contrasts with that information.