Robert only consumes x and y, and his indifference curves have the usual convex shape. consider the consumption bundles (3, 9), (6, 6), and (9, 3) (hint: the consumption bundles completely exhaust robert's income). if robert is indifferent between (3, 9) and (9, 3), then:

Then consumption bundle (3,9) and (9,3) will lie on the same indifference curve.

Since his consumption bundles completely exhaust his income , therefore the indifference curve will be tangential to the budget constraint.

Explanation:

Given : Robert only consumes X and Y, and his indifference curves have the usual convex shape.

Consumption Bundles (3, 9), (6, 6), and (9, 3).

If Robert is indifferent between (3, 9) and (9, 3), then: consumption bundle (3,9) and (9,3) will lie on the same indifference curve.

Also, since his consumption bundles completely exhaust his income , therefore the indifference curve will be tangential to the budget constraint.

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.'