Final answer:
Adenine is found in all members of the group D: Proteins, ATP, and DNA. Adenine is a purine base and an essential component of DNA and RNA.
Step-by-step explanation:
The nitrogenous base adenine is found in all members of the group D. Proteins, ATP, and DNA. Adenine is one of the four nitrogenous bases found in DNA and RNA, along with guanine, cytosine, and thymine in DNA or uracil in RNA. Adenine is a purine base, which means it has a double ring structure. It is an essential component of DNA and RNA and plays a crucial role in their structure and function.