A humble request – Please give KUDOS if you like the explanation.
The answer is A.
Outshining the Panama Canal or even the Empire State Building as an incredible construction feat, the Hoover Dam built to tame the Colorado River, one of America’s most powerful rivers, is more than 726 feet tall and took 21,000 workers more than two years to finish.
Let us first dissect the sentence.
Outshining the Panama Canal or even the Empire State Building as an incredible construction feat, - This part of the sentence is used to modify the noun hoover dam.
the Hoover Dam
built to tame the Colorado River, - modifies Hoover Dam
one of America’s most powerful rivers, - modifies Colorado River
is more than 726 feet tall and took 21,000 workers more than two years to finish.
HD is more than …and took… - SV pair
(A) the Hoover Dam built to tame the Colorado River, one of America’s most powerful rivers, is more than 726 feet tall and took 21,000 workers more than two years to finish
(B) the Colorado River, one of America’s most powerful rivers, was tamed by the Hoover Dam that was built to be more than 726 feet tall and took 21,000 workers more than two years to finish it
Outshining the Panama Canal or even the Empire State Building as an incredible construction feat, - This part of the sentence is used to modify the noun Colorado river which is incorrect.
Also, this is a passive sentence. The rest of the sentence is a train Wreck.
(C) it took 21,000 workers more than two years to finish the 726-foot-tall Hoover Dam that would tame the Colorado River, one of America’s most powerful rivers
This choice is a contender. Hoover dam is far away from the modifying phrase ‘Outshining…feat’
(D) for more than two years, 21,000 workers built the 726-foot-tall Hoover Dam that would tame the Colorado River, one of America’s most powerful rivers
Outshining the Panama Canal or even the Empire State Building as an incredible construction feat, - This part of the sentence is used to modify the noun HD and not for more than two years..
(E) more than two years were needed to complete the 726-foot-tall Hoover Dam that 21,000 workers built to tame the Colorado River, one of America’s most powerful rivers
Outshining the Panama Canal or even the Empire State Building as an incredible construction feat, - This part of the sentence is used to modify the noun HD and not for more than two years..
This is a worst choice.