Answer: b) background assumptions
Step-by-step explanation:
In terms of ethnomethodology, background assumptions are the ideas of general life that are taken for granted by the people to breach it. It is the method through which people understand assumption's experience,sense value and influence in daily life by risking it on own self.
Other options are incorrect because social features, sign, social concept and facts are not the basic thoughts or assumptions that can be broken or challenged by taking for granted .Thus, the correct option is option(b).