Answer: Inefficient.

**Explanation:** - **Option A (Correct):** Under all forms of market efficiency, past trading data are already incorporated into current prices, making it impossible for investors to predict future price movements by analyzing historical prices or patterns. Therefore, if investors can predict future asset prices based on past prices, the market is deemed inefficient. - **Option B (Incorrect):** In a weak-form efficient market, security prices reflect all past market data, including historical prices and trading volumes. If the market were weak-form efficient, past trading data would already be reflected in current prices, and investors would not be able to predict future price changes using historical data. - **Option C (Incorrect):** In a semi-strong-form efficient market, all publicly available information is already reflected in security prices. If the market were semi-strong-form efficient, past trading data would also be incorporated into current prices, preventing investors from predicting future price changes based on historical data. This question tests the understanding of market efficiency forms and their implications for investment strategies.

Author: LeetQuiz Editorial Team