Question: On October 1, NAME_1 mailed to NAME_2 an offer to sell a tract of land located in Summerville for $13,000.  Acceptance was to be not later than October 10.  NAME_2 posted his acceptance on the 3rd of October.  The acceptance arrived on October 7.  On October 4, NAME_1 sold the tract in question to NAME_3 and mailed to NAME_2 notice of the sale.  That letter arrived on the 6th of October, but after NAME_2 had dispatched his letter of acceptance.  Which of the following is correct?
A: There was a valid acceptance of the NAME_1 offer on the day NAME_2 posted his acceptance.
B: NAME_1's offer was effectively revoked by the sale of the tract of land to NAME_3 on the 4th of October.
C: NAME_1 could not revoke the offer to sell the land until after October 10.
D: NAME_2's acceptance was not valid since he was deemed to have notice of revocation prior to the acceptance.
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option.