Oxygen and glucose
are reactants in the process of cell respiration.
Explanation
In the cellular respiration, Glucose is required in the formation of ATP whereas oxygen is required for the converting glucose into ATP. One glucose molecules gives 2 ATP.
In other living beings oxygen enters when we breath but glucose enters when we eat something. One molecule of glucose and 6 molecules of oxygen gives 6 molecules of and 6 molecules of water.
Adenine (A) and Thymine (T) are base-pairs, alongside Cytosine (C) and Guanine (G). Only A - T or G - C are base-pairs in DNA strands, you will never see Adenine (A) and Cytosine (C) together in a DNA or RNA strand.