单项选择题

Many a plan ______ to fight against pollution.

A．have been worked out
B．have been worked on
C．has been worked out
D．has been worked on

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单项选择题

Both his brother and his sister ______ busy with their homework.

A．is
B．are
C．am
D．be

单项选择题

Tony ______ yesterday if he were really serious about his work.

A．ought to come
B．should come
C．must have come
D．should have come

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