单项选择题

The influenza discovered by a doctor in Singapore is caused by （）

A．a new type of virus
B．type A virus
C．a sub-group of type B virus
D．a virus only existing in Asia

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填空题
A. trail B. certain C. again D. faint
单项选择题
--Have your students ever seen the silent film --No, they are too young （） the old film.

A. to seeing
B. have seen
C. to have seen
D. to have not seen
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