The signaling principle in finance would suggest that when a firm announces a plan to repurchase outstanding shares $($stock$),$ this action could be a signal that the firm's managers $($insiders$)$ believe the firm's shares are:

a$.$ neither of the other alternative answers, as this action would not signal anything about management's sentiments with respect to the stock price.

b$.$under$-$valued in the market

c$.$over$-$valued in the market