you have been cleared for the straight-in localizer approach for runway 13l at dal. prior to reaching the final approach fix, atc advises you the rvr is not available and that the visibility is 1/2 sm. you may a. request the ils approach and disregard the rvr value. b. convert the rvr to statute miles and use the next higher minimums. c. convert the rvr to statute miles and continue the approach.