econ 100a final practice In a perfectly competitive market, firms take the market price as a given, which implies that the market demand is:

Perfectly elastic

Explanation:

A perfect competition is characterized by many buyers and sellers of homogenous goods and services. Market prices are set by the forces of demand and supply. There are no barriers to entry or exit of firms into the industry.

In the long run, firms earn zero economic profit. If in the short run firms are earning economic profit, in the long run firms would enter into the industry. This would drive economic profit to zero.

Also, if in the short run, firms are earning economic loss, in the long run, firms would exit the industry until economic profit falls to zero.

the market demand is perfectly elastic because goods in a perfect competition are identical, if a producer increase its price, consumers would stop demanding for the producer goods and shift to another producer.

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.'