Bacteria that are found in extreme environments are categorized as

a. archaea

b. bacteria

c. eukaryotes

d. protists

Archaea

Explanation:

The three domains of life are prokarya, eukarya and archaea. Archae and prokarya includes the unicellular organism and eukarya involves the unicellular eukaryotes and multicellular organism.

The archaea shares more common characteristics to eukarya than with the prokarya. The bacteria that are present in the extreme environment like acidophiles and thermophiles are involved in the archaea.

Thus, the correct answer is option (a).