Choice A is the best answer. Lines 18-22("Within...lanthanum.") suggest that space mining may help meet "earthly demands for precious metals . . . and the rare earth elements vital for personal electronics." In this statement, the author is stat-ing materials ("metals," "earth elements") that may be gathered as a result of space mining, and that these materials may be important to Earth's economy.
Choices B, C, and D do not provide the best evidence for the answer to the previous question. Choice B is incorrect because lines 24-28("They... projects.") focus on an "off-planet economy" but never address positive effects of space mining. Choice C is incorrect because lines 29-30("In... commodity.") suggest the relative value of water found in space. Choice D is incorrect because lines 41-44("Companies... machinery.") state that space mining companies hope to find specific resources in lunar soil and asteroids but do not address how these resources are important to Earth's economy.