不属于半导体红外激光打印机的激光光谱波长的是（）
A．632.8nm
B．670nm
C．790nm
D．820nm
E．780nm
参考答案：A
In ____, he began to learn Russian, when he was in ______.
A．1970; the 50’s
B．the 1970; his 50s
C．the 1970s; his fifties
D．1970s; his fifties
We left Xi' an _.___ a very hot summer afternoon.
A．on
B．in
C．during
D．by
