Behavioral finance argues that: O a. investors are rational and the failure to uncover successful trading rules or traders cannot be taken as proof of market efficiency O b. the failure to uncover successful trading rules or traders can be taken as proof of market efficiency O c. even if security prices are wrong it may be difficult to exploit them O d. even if security prices are wrong, it may be difficult to exploit them, and the failure to uncover successful trading rules or traders cannot be taken as proof of market efficiency Oe. All of these are correct