单项选择题

Edmund Halley figured out the orbit of ______.

A．some different comets appearing several times
B．the same comet appearing at different time
C．three different comets appearing three times
D．several comets appearing at the same time

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热门试题

单项选择题

Halley made his discovery ______.

A．by doing experiments
B．by means of his own careful observation
C．by using the work of other scientists
D．by chance

单项选择题

This passage in general is about ______.

A．Halley and other scientists
B．the orbit of a comet
C．Newton and Halley
D．Halley and his discovery