TOEFL Reading: ETS-TOEFL阅读机经 - 043846525GS3HZRZL$

According to paragraph 6, which of the following is NOT true of the connection between mammals and oxygen? A. Mammals are able to survive only because oxygen levels are relatively high. B. Mammals first emerged when atmospheric oxygen levels reached 10 percent. C. A mammal's unborn child receives oxygen through the mother's placenta. D. Mammals use a lot of oxygen partly because they are warm-blooded.