Explanation:

In arbitrage pricing theory (APT), an arbitrage opportunity exists when a trader can earn a positive net profit with:

• No risk: The position should be risk-free, meaning the outcome is certain regardless of market movements
• No net investment: The trader doesn't need to commit any capital upfront

This is the fundamental definition of pure arbitrage - earning risk-free profits without any initial investment. Option A correctly captures both conditions, while options B and C violate one of these essential requirements.