The correct answer is: C. weak form efficiency.
Weak form efficiency is a market efficiency hypothesis that states that all past price and volume information is fully reflected in the current market price. This means that it is not possible to earn excess returns by using past price data to predict future prices.
Market efficiency is a concept in financial economics that states that asset prices reflect all available information. This means that it is not possible to consistently outperform the market by using publicly available information.
Semi strong form efficiency is a market efficiency hypothesis that states that all publicly available information is fully reflected in the current market price. This means that it is not possible to earn excess returns by using publicly available information to predict future prices.
Strong form efficiency is a market efficiency hypothesis that states that all information, including private information, is fully reflected in the current market price. This means that it is not possible to earn excess returns by using any information to predict future prices.
Here is a diagram that summarizes the different types of market efficiency:
I hope this helps! Let me know if you have any other questions.