Explanation:

An arbitrage opportunity must satisfy three key requirements:

1. Risk-free (A) - No uncertainty about the outcome
2. Zero net investment (B) - No initial capital required
3. Profitable (C) - Positive return guaranteed

However, arbitrage does not require a return in excess of the risk-free rate (D). In fact, arbitrage opportunities typically offer returns that are very close to zero in efficient markets, as they are quickly exploited by market participants. The key characteristic is that the return is guaranteed and risk-free, not necessarily that it exceeds the risk-free rate.