In 1953, Stanley Miller and Harold Urey built a model of Earth's early atmosphere by mixing gases that were thought to have been there. They
exposed the gases to an electric current to simulate lightning. The liquid that
condensed during the experiment contained amino acids.

What was the significance of their results?

A. Miller and Urey showed that lightning was necessary for life to
form on Earth.
B. Miller and Urey showed that spontaneous generation was
possible.
C. Miller and Urey showed that inorganic compounds could combine
to form the building blocks of living cells.
D. Miller and Urey showed that all life evolved from a single common
ancestor.

C. Miller and Urey showed that inorganic compounds could combine  to form the building blocks of living cells.

Explanation:

The Miller and Urey were the two scientists who created the atmospheric conditions that were expected to be present on primitive earth. They demonstrated that several organic compounds have been formed spontaneously from the inorganic compounds like water, ammonia, methane and others.

The exposure of mixture of inorganic compounds by the lightening lead to the formation of organic molecules like amino acids which are the building blocks of life. This was similar to the penetration of earth atmosphere by UV radiation producing the organic compounds from inorganic molecules.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.