TOEFL Reading: ETS-TOEFL阅读机经 - DWADI1HR1O3S4VKGL$

Select the TWO answer choices that, according to paragraph 2, are true of the swimming behavior of ducks and muskrat. To receive credit you must select TWO answer choices. A. Ducks and muskrat require far more energy to swim on the surface than fish of a similar size require to swim underwater. B. Ducks and muskrat must overcome drag produced by the bow wave when swimming both on the surface and submerged. C. Ducks and muskrat spend as much time underwater as possible in order to use less energy in swimming. D. Ducks and muskrat are more efficient when swimming underwater than when swimming on the surface.