Choice A is the best answer. In lines 60-66(Passage 2, Paragraph 3) the author presents some environmental arguments against space mining: "[space] is not ours to despoil" and we should not "[glut] ourselves on space's riches." The author then sug-gests that these environmental arguments will be hard to "hold," or maintain, when faced with the possible monetary rewards of space mining: "History suggests that those will be hard lines to hold . . ." (line 68, "History suggests...the public").
Choices B, C, and D are incorrect because in this context, "hold" does not mean grip, restrain, or withstand.