On average, about 3,500 new mobile homes are sold every month at an average price of $40,000. in 2013 average income in the united states rose and, all else equal, mobile home sales decreased. from the information given, it is reasonable to conclude that mobile homes:

Mobile homes are a substitute good.

Explanation:

Substitute goods are goods in which one of them can be used instead of the other. Their demands are related, so if a variable changes, the demand for those goods will also change. Generally the variables that give way to these changes in demand are the price of the good or the income of the consumer.

In this case, the income of consumers increased, so the demand for mobile homes decreased, this means that mobile homes are a substitute for a standard house, that is, having more income consumers will replace mobile homes by standard houses being these more expensive.

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.'