A price ceiling . A. set below the equilibrium price encourages illegal trading in a black market B. is a regulation that makes it illegal to offer less than a specified quantity of a good or service for sale C. is a regulation that makes it illegal to offer more than a specified quantity of a good or service for sale D. always prevents the price from regulating the quantities demanded and supplied

A. set below the equilibrium price encourages illegal trading in a black market

Explanation:

Price Ceiling is maximum mandated price at which a good can be sold in market. It is usually set below equilibrium price level, to protect consumers from overpricing under free markets.

Price ceiling at a lower price creates Excess Demand or shortage of good (Demand > Supply) , as demand is more at lower prices but supply is less at lower prices. This shortage leads to sellers selling in Black markets at illegal higher price, to buyers having unsatisified demand & higher willingness to pay.

ans.

heterothermic organisms include those organisms that can switch between homeothermic (having body temperature higher than environment) and poikilothermic (having variation in internal body temperature) strategies.

some migratory birds show heterothermy as they decrease their metabolic rate during cold nights to keep their body temperature low. drop in metabolic rate allows increase in production efficiency of birds that reduces the internal body temperature to make it equal to external cold temperature during cold nights.

thus, the correct answer is 'birds allow their temperature drop in order to increase their production efficiency.'