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

[Q]: Passage: The alkaline earth metals include beryllium, magnesium, calcium, strontium, and barium. Strontium and barium react with air and must be stored in oil. Answer: alkaline earth metals
[A]: Beryllium, magnesium, calcium, strontium, and barium are classified as what type of metals?

[Q]: Passage: Mutations have many possible causes. Some mutations occur when a mistake is made during DNA replication or transcription. Other mutations occur because of environmental factors. Anything in the environment that causes a mutation is known as a mutagen . Examples of mutagens are shown in Figure below . They include ultraviolet rays in sunlight, chemicals in cigarette smoke, and certain viruses and bacteria. Answer: mutation
[A]: What is it called when a mistake occurs in dna replication.

[Q]: Passage: Carbon has four valence electrons, so it can achieve a full outer energy level by forming four covalent bonds. When it bonds only with hydrogen, it forms compounds called hydrocarbons. Answer: four
[A]:
How many valence electrons does carbon have?