TOEFL Reading: ETS-TOEFL阅读机经 - 33ITR6YJL7254HJ5L$

The discussion of bird migration in paragraph 6 implies that A. birds that can navigate by sensing Earth's magnetic field cannot navigate using the Sun or stars B. pigeons can navigate when the Sun or stars are obscured by clouds C. magnetite is likely to be part of the navigational system of only a few species of birds D. birds' navigation using magnetite is not as accurate as their navigation based on the Sun or stars