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

As far as we can tell from the story, Agatha Christie ()

A．had never met this baby
B．had spent a long time studying the baby' s illness
C．visited the baby both in Deleville and London
D．gave the nurse some advice on, the telephone

单项选择题

When the baby was first sent to the hospital in London, her illness was considered to be ()

A．quite easy to treat
B．the result of thallium poisoning
C．a common one
D．extraordinarily serious