单项选择题

Programmed instruction received its major impetus from the work of behaviorist J. H. Skinner, who after years of research,______ a practical system in 1954.

A．described
B．derived
C．imitated
D．devised
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单项选择题
When her report came, she found that she had received three D' s and two C' s . Soon she began to recall some of the errors she______ on her test.
A．should have made
B．might have made
C．would have made
D．could make
单项选择题
Work in parapsychology,______, has attracted a relatively small number of scientists.
A．is a very controversial field
B．which a very controversial field is
C．a very controversial field
D．a field very controversial which
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