I had the same question, it's most likely B.
Answer:
Carbon
Explanation:
Carbon has four electrons in its valence shell, so it generally shares it in a covalent bond. This element needs four electrons to be stable, so it can form single (such as the bond with hydrogen), double (such as the bond with oxygen) or triple bonds (such as the bond with nitrogen).
It can also form bonds with other carbon, and they can form longs chains, that's why there are a lot of organic compounds (the compounds with carbon). Carbon can form rings too, such as in benzene.
