单项选择题

According to the passage the new telephone communication system （）

A．has been put into actual use
B．was first put into actual use in 1977
C．had been repeatedly experimented on before 1977
D．was put on experiment in 1977

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单项选择题

54（）

A．enormous
B．human
C．undesirable
D．generous

单项选择题

53（）

A．employ
B．emphasize
C．explain
D．comprise