Given a scientific passage and an answer, generate a question for the given answer.
--------
Question: Passage: It was known that DNA is composed of nucleotides , each of which contains a nitrogen-containing base, a five-carbon sugar (deoxyribose), and a phosphate group. In these nucleotides, there is one of the four possible bases: adenine (A), guanine (G), cytosine (C), or thymine (T) ( Figure below ). Adenine and guanine are purine bases, and cytosine and thymine are pyrimidine bases. Answer: nitrogen

Answer: What does the base of a nucleotide within dna consist of?

Question: Passage: Images in a plane mirror are reversed left and right but not reversed top and bottom. Answer: plane mirror

Answer: Images in what type of mirror are reversed left and right but not reversed top and bottom?

Question: Passage: Shield volcanoes commonly form above hotspots in the oceans. Answer: volcano

Answer:
The shield type of what phenomenon commonly forms above hotspots in the oceans?