单项选择题

Newly-found fossilized tracks in Alaska proved that dinosaurs' migration between Asia and North America took place ______.

A．much earlier than experts previously thought
B．much later than experts previously thought
C．after Asia became an independent continent
D．sometime around 25 million years ago
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单项选择题
Witmer’s research leads people to believe ______.
A．Tyrannosaurus Rex had lips and Triceratops had cheeks
B．dinosaurs might have looked like mammals such as sheep
C．dinosaurs might not have looked like what we thought
D．dinosaurs must have looked like birds or crocodiles
单项选择题
The discovery of a new type of ceratopsian dinosaur suggests ceratopsians ______.
A．migrated to North America around 70-80 million years ago
B．arrived in Asia from Noah America about 90 million years ago
C．originated in Asia and later migrated to North America
D．could have moved to Asia from North America long ago
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