Which of the following is a TRUE statement about market efficiency?

a-The reason executives and board of directors are reluctant to use "insider information" because security markets are strong-form efficient.

b-If security markets are weak-form efficient, investors cannot solely use previous price movements to earn excess returns.

c-According to the "January effect," prices of small stocks in the past have experienced abnormal price declines in January.

d-Semistrong-form market efficiency implies that a security market is also strong-form efficient.