Which of the following did Stanley Miller place in his experimental system to show that organic molecules could have arisen from inorganic molecules on the primitive earth?

In 1953, Stanley Miller and Harold Urey did an experiment to test Oparin and Haldane’s ideas. They found that organic molecules could be spontaneously produced under reducing conditions thought to resemble those of early Earth.
Miller and Urey built a closed system containing a heated pool of water and a mixture of gases that were thought to be abundant in the atmosphere of early earth. To simulate the lightning that might have provided energy for chemical reactions in Earth’s early atmosphere, Miller and Urey sent sparks of electricity through their experimental system. After letting the experiment run for a week, Miller and Urey found that various types of amino acids, sugars, lipids and other organic molecules had formed. Large, complex molecules like DNA and protein were missing, but the Miller-Urey experiment showed that at least some of the building blocks for these molecules could form spontaneously from simple compounds.