If you live in a big city, you may take for granted the tall buildings. Even if you live in a smaller town, you probably have seen tall buildings. These buildings have existed for a little more than 100 years. Before that, materials were not strong enough to hold up tall structures. In older buildings, the walls carried the weight of the upper stories. Therefore, a building could have only a limited number of floors. With new materials such as ready-made steel and concrete blocks, builders could shift the weight from walls to columns and beams.
Cranes and other machines were invented to allow the lifting of huge blocks and pieces of steel high into the sky. The elevator car, although dating from the nineteenth century, became more important because of taller buildings.
Even with these advances, some critics say that ideas and methods in the construction industry do not change quickly. However, you can judge for yourself.

Which sentence best states the main idea for a summary of this passage?

Changes in materials made it possible for workers to build taller buildings.

Some people claim that advances in construction methods happen slowly.

The elevator became more important when tall buildings were made.

In the past, building materials could not hold up tall buildings.