Explanation
Correct answer: B.
Choice B is the best answer. The passage explains that heliographs “were largely effective only during the daytime” and that “the range of the device depended on factors such as the opacity of the air and line of sight.” These constraints would have greatly limited the use of the heliograph, so we can infer that this would have been a reason to replace it with new technology.
Why the other choices are wrong
Choice A
Choice A is incorrect. The passage doesn’t discuss the production and maintenance of heliographs, so there’s no basis for this inference.
Choice C
Choice C is incorrect. The passage doesn’t mention any “other purposes” that a heliograph wouldn’t work for, so there’s no basis for this inference.
Choice D
Choice D is incorrect. The passage doesn’t mention knowledge of Morse code as a particular problem with the use of heliographs, so there’s no basis for this inference.