Why is the answer A and not B?

Hi @capoleway@gmail.com Happy to help! The author concludes that it is not surprising that environmentalists fail to consider the negative effects of space flight. Why? Because space-based satellites allow for earlier observation of environmental issues meaning that these issues can be addressed before they become crises. Answer choice (B) is incorrect because the author suggests the opposite in their final sentence, noting that the damage spacecraft may cause to the ozone layer "could be serious enough to warrant discontinuing space flight." Answer choice (A) is correct because it directly supports the author's conclusion. People (environmentalists) tend to ignore possible objectionable consequences (impacts of spacecraft) of actions (space flight) that support their activities (conservation and addressing environmental issues). Hope this helps! Please let us know if you have any further questions.

I ruled out A because "tends to ignore" sounds stronger and more of a conscious decision than "fails to consider"

While there might be a slight difference in degree of intentionality in those phrases, they are clearly pointing in the same direction, and are expressing more or less the same idea. I think it's critical to recognize that the ideas expressed are infinitely more important that the wording, and that an idea can be expressed in a number of different ways. Here, we could absolutely describe someone who is ignoring something as failing to consider that thing.