Magoosh Practice CR question- Interstate Bridge over the Apache River

Glad that my explanation made sense. Btw, here, in the GMATClub community we have a special way to thank someone, its known as 'Kudos'
And it is just one click away on the left side pane of the original message that helped you

Dear bhavikagoyal2009,

I'm happy to respond.

My friend, I am going to chide you on attention to detail. First of all, the OA is (D), not (E). See here.

Also, it is completely unfair to conflate "community activists" with "communists." That mistake would garner either riotous laughter or harsh criticism if you made it in conversation among native speakers.

community activists = residents of a community, such as a town, or speak out as advocates for public improvements to the community
communists = people who, in accordance with the teachings of Marx, advocate a violent worker's revolution to overthrow not only the government but the entire economic superstructure

Community activists are likely to speak up, say, about a bridge in their community becoming old or unsafe. Communists are people who might blow up the bridge as an act of protest! I am being a little extreme in my descriptions, because in the modern world there are some peaceful non-violent communists, but communism always has much much bigger plans and bigger scope than community activism, which is always locally focused. These are two very different ideas.

Now, as to your question, why can't (B) be right? Why can't the community activist's conclusion be the argument's conclusion.

Think about it. What is the basis of the community activist's conclusion? These people are simply looking at the bridge, looking at it as non-scientific non-specialist, and drawing a conclusion about what they see with their eyes.

What is the basis of the second BF statement? These are academic scientists, and they do an "extensive analysis"--we don't know, but it's likely that these scientists used scientific measurements and/or precise scientific calculations. They published an "academic study," that is to say, an article in a peer-reviewed journal that has to conform to certain standards of evidence. The conclusion that scientists make with scientific data is considerably stronger than the conclusion that non-scientists infer simply by looking at something.

Even the nature of the conclusion is telling. The community activists were looking from the outside and could only see the outside: they saw a lot of rust on the surface and thought this meant that most of the bridge had rusted through. By contrast, the scientists had means to detect how much below the surface was rusted, and it turns out, most of what is below the surface is not rusted; moreover, the surface rust protects this underlying unrusted metal.

The community activists were looking at the surface and the scientists were looking at the deep structure. Of course the scientists' conclusion was better supported.

Does all this make sense?
Mike