Q21 - During construction of the

[tzyc]

From this part: Cooper telegraph to freeze the project...I thought Cooper was not there (so he needed to telegraph) and chose (B), but is it incorrect because the absence may not actually cause the breaking off?

Thank you

[ohthatpatrick]

I think you got it. We can certainly infer that Cooper was absent from the site, but we can't infer that his absence caused the breaking off.

The most direct cause of the bridge collapse that we are told is that the bridge's cantilever was deflecting downward by a fraction of any inch.

We can't infer that, had Cooper been present, the cantilever would / would not have deflected downward by a fraction of an inch.

So it's too much of a leap to pick (B) (and too much blame to place on poor Cooper).

=== other answers ===
(A) "unsafe" is too extreme ... we don't have any information about the safety of any completed bridges prior to 1907.

(C) "inadequate" is extreme and out of scope ... we don't know WHY "rules of thumb" were used more than thorough mathematical analysis.

(D) "only" is too extreme ... we can't safely infer that ONLY math could have saved the day.

Hope this helps.