The discount rate is:
a. the interest rate banks charge other banks for loans.
c. the percentage amount that the federal reserve discounts when it buys government securities.
b. the interest rate the federal reserve charges for loans to commercial banks.
d. a tool of fiscal policy.

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.'