Given a scientific passage and an answer, generate a question for the given answer.

Input: Consider Input: 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

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

Input: Consider Input: Passage: Optical telescopes are designed to collect visible light. The two types of optical telescopes are reflecting telescopes and refracting telescopes. Answer: reflecting and refracting

Output: What are the two types of optical telescopes?

Input: Consider Input: Passage: The mouth also begins the process of mechanical digestion . Sharp teeth in the front of the mouth cut or tear food when you bite into it (see Figure below ). Broad teeth in the back of the mouth grind food when you chew. Food is easier to chew because it is moistened by saliva from the salivary glands. The tongue helps mix the food with saliva and also helps you swallow. After you swallow, the chewed food passes into the pharynx. Answer: mouth
Output: Where does mechanical digestion begin?