Answer:
Deuterium, (D, or 2H), also called heavy hydrogen, isotope of hydrogen with a nucleus consisting of one proton and one neutron, which is double the mass of the nucleus of ordinary hydrogen (one proton). Deuterium has an atomic weight of 2.014
Explanation:
The term which describes any relationship in which two species live closely together is called SYMBIOSIS.
Answer: D. Peptides
