Read the two paragraphs below from the section "A missed train and a dream".In 1867, when Mendeleev began writing "Principles of Chemistry," he set out to organize and explain the elements. He began with what he called the "typical" elements: hydrogen, oxygen, nitrogen, and carbon. Next he included the halogens. These had low atomic weights, reacted easily with other elements, and were readily available in nature. Chlorine — used to keep pools clean — is a halogen. Mendeleev begun using atomic weights as a principle of organization, but these alone did not present a clear system. At the time, elements were normally grouped in two ways: either by their atomic weight or by their common properties, such as whether they were metals or gases. Mendeleev’s breakthrough was to see that the two could be combined in a single framework. Which BEST explains how the two paragraphs help to develop the central idea of the article?AThey identify the elements that Mendeleev considered to be typical elements. BThey give background information about how Mendeleev first started creating a system to organize the elements. CThey provide information about how Mendeleev came to learn that he could combine the two grouping systems. DThey make a connection between Mendeleev's work in the 1800s and today by describing the modern use of chlorine.