B.THIS IS THE ONLY CHOICE THAT MAKES SENSE IN THEAUTHOR DOES INTRO...

28. b.This is the only choice that makes sense in theauthor does introduce the single-payer systemcontext of the sentence. A context clue can befound in lines 1–2, which says, “ . . . teens are(choice a) and does compare the U.S. health-care system to Canada’s (choice b), neither ofnot vigorously active . . .”