[Ch5-1] A fixed cost, within the relevant range and in the short term, Select one: O a. is fixed and unchanging. O b. may vary in response to sudden changes in weather or other external conditions or events. O c. remains unchanged per unit with changes in the production activity level. O d. may vary in total with changes in the firm's production. Clear my choice [Ch5-1] A variable cost, within the relevant range and in the short term, Select one: O a. varies per unit at every activity level. O b. varies in total with changes in the local economic activity level or condition. O c. varies per unit directly and proportionately with changes in the activity level. O d. varies in total directly and proportionately with changes in the activity level