Once Management Announces That It Will Buy Back One Million

Once management announces that it will buy back one million shares over a given time period,as circumstances become appropriate,

A) it is legally obligated to buy all one million shares back.
B) it is not legally obligated to buy any or all one million shares back.
C) it must buy back the number of shares that are equal to income in a given year (up to one million shares) .
D) it must buy back the number of shares that are equal to income minus common stock dividends in a given year (up to one million shares) .