What is the possibility of a long-run equilibrium for a monopolistically competitive firm wherein economic profits are zero is based upon the assumption of: a. rising marginal costs
b. the weakness of barriers to entry
c. product differentiation
d. a perfectly elastic demand curve

places of higher salinity. there are parts of the ocean where hardly any rain falls but warm dry winds cause lots of evaporation. this evaporation removes water – when water vapour rises into the atmosphere, it leaves the salt behind, so the salinity of the seawater increases. this causes the seawater to become denser.