Which invention made the building and use of skyscrapers feasible?

a. mass transit c. zoning laws

b. elevators d. suburbs

The answer to this question is B. Elevators

One of the reason why skyscrapers were not popular before the invention of elevators was that it took too much energy to move from the groud floor to the upper floor with the stairs alone.

After the invention of elevators, we eliminate this problem and people could move from ground floor to upper floor with only little effort.