Before revision:  b ) a fundamental component proportional to the log earnings over price ratio at time zero  , from which the actual stock price may deviate as an effect of random external disturbances, and c ) a driving component ensuring the diffusive behaviour of stock prices.
After revision:  b ) a fundamental component proportional to the log earnings over price ratio at time zero , from which the actual stock price may deviate as an effect of random external disturbances, and c ) a driving component which ensures the diffusive behaviour of stock prices.