Final answer:
People primarily obtain nitrogen by eating meat and vegetables, as plants absorb nitrogen converted by nitrogen-fixing bacteria, which is then passed through the food chain.
Step-by-step explanation:
The way people get nitrogen is primarily through the consumption of meat and vegetables. The air we breathe is predominantly composed of nitrogen gas (N₂), but this version of nitrogen is largely inaccessible to humans and other animals directly because they cannot break the strong triple bond that nitrogen gas molecules have.
However, nitrogen-fixing bacteria can convert atmospheric nitrogen into compounds that plants can use, such as nitrates and ammonium. Subsequently, animals get nitrogen by ingesting plants or other organisms that have consumed plants. Therefore, the correct answer to how people obtain nitrogen is through option 'c. eating meat and vegetables.'