Limonene's natural source in citrus

Steps:

• Identify limonene as a monoterpene hydrocarbon.
• Recall its primary natural occurrence in plant essential oils.
• Link to citrus fruits, especially peels, where it's abundant.
• Confirm lemons as a key source via chemical extraction.

Why C is correct:

• C states limonene is a component of lemon oil, matching its definition as the main terpene in citrus peel oils (up to 90% in lemons).

Why the others are wrong:

• A: Incorrectly claims it's synthetic only, ignoring natural plant origins.
• B: Falsely attributes it to flowers, not fruit peels.
• D: Wrongly specifies oranges exclusively, as it's in multiple citrus including lemons.

Not enough information for full context, but C fits standard knowledge.

Final answer: C