Which one of the following is not true about variable costs? Select one: O a. They are used to calculate the contribution margin O b. They are constant per unit O c. None of the given answers O d. They are constant in total To earn summer money, Ahmed could work as a taxi driver, or he could work at a local grocery store. Which of the following is an opportunity cost of working as a taxi driver? Select one: O a. The wages he could have earned working at the grocery store. O b. None of the given choices O c. The time spent in driving the taxi. O d. Depreciation on the taxi. O e. Cash paid for fuel to run the taxi