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
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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
单项选择题
Halley made a surprising, but correct prediction in the year ______.
A．1704
B．1705
C．1706
D．1707
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