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

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
How many valence electrons does carbon have?

Passage: Amines are weak bases due to the presence of a lone pair of electrons on the nitrogen atom. This lone pair can attract the hydrogen atom from a water molecule, causing the bond between it and the oxygen atom to break. The resultant products are the conjugate acid of the amine and the hydroxide ion. Answer: electrons
Amines are weak bases due to the presence of a lone pair of what on the nitrogen atom?

Passage: The main functions of the male reproductive system are to produce sperm and secrete testosterone. Answer: male reproductive system
Producing sperm and secreting testosterone are the main functions of what system?