单项选择题

It is thought that modern corn may be a______of teosint and other wild species that no longer exist.

A．hybrid
B．combination
C．compound
D．mixture
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单项选择题
The doctor’s efforts were______. The patient refused to accept the treatment.
A．of no avail
B．in no avail
C．by no avail
D．on no avail
单项选择题
The wife of Steve Carvey, the baseball star, ______about being left alone too often.
A．bitterly has complained
B．has bitterly complaining
C．has been complained bitterly
D．has been complaining bitterly
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