27, proni se po (a) variable costs (b) explicit costs. (c) implicit costs (d) marginal costs 28. All points on or below a budget constraint (a) Are attainable with the given income. (b) Are equally desirable. (c) Represent market basket combinations that exhaust the income available. (d) Are described, in part, by a, b, and c above. (e) None of the above