In light of your budget, which device is the best buy for communicating with your fellow student in the coffee shop? Which device is the best choice for communicating with your fellow student located at your school? What trade-offs do you need to consider, such as size of device vs. Features?

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.'

i think the answer to your question is b. directive