The right option is; B- The carbon cycle ensures that living things have a continual source of hydrogen.
The carbon cycle is a process that describes how carbon compounds moves between living organisms and their environment. Carbon is an important element and the fundamental building block of all living organisms. The carbon cycle ensures continual availability of other elements and compounds such as hydrogen and oxygen. Carbon is mainly available in the atmosphere as carbon dioxide, and also less available as important gases, such as methane (hydrocarbon). In living organisms, all hydrogen apart from the one present in water is in form of hydrocarbons.
