Given here are five sentences. The first sentence is in the correct order, while the rest of the sentences are jumbled. Pick the option that gives the correct order.

A. When Mendeléev started his work, 63 elements were known. 

B. Among chemical properties, Mendeléev concentrated on the compounds formed by elements with

C. He examined the relationship between the atomic masses of the elements
and their physical and chemical properties.

D. oxygen and hydrogen. He selected hydrogen and oxygen as they are

E. very reactive and formed compounds with most elements