In mammals, heart size tends to be proportional to body weight while heart rate is inversely proportional to body weight. What is the most probable explanation for pygmy shrews having unusually large hearts but an unusually slow heart rate?
A) Pygmy shrews are very active so they need large hearts.
B) It is possible that the heart rate of shrews has reached its absolute limitation, so a large heart can pump more blood with each beat.
C) Since pygmy shrews are tiny, their heart size differs from other mammals and their heart rate is slow when they are at rest.
D) The heart size of pygmy shrews varies depending on latitude.
Answer: B
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