The methanogens a. are part of the archaea. b. oxidize hydrogen gas to produce methane. c. appear only in aerobic environments. d. use oxygen as a terminal electron acceptor. e. are part of the archaea and oxidize hydrogen gas to produce methane.

Are part of the Archaea AND oxidize hydrogen gas to produce methane. (Ans. E)

Explanation:

Methanogens are micro-organism which belongs to archaea, and they are obligate anaerobes which can survive without oxygen. They are producing methane as a byproduct of their metabolism.

Methanogen belongs to archaea domain which are extremophiles such as hot temperature, or highly salty environment. Methanogens can live in guts of cow, and in muck from sewage treatment plants.

Methanogens consume carbon dioxide and hydrogen and release methane gas. They are basically two types in shapes coccus (circle shape) and bacillus (rod shape).

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

b. lithosphere, asthenosphere, mesosphere   is the answer most likely