2) 这篇论文总结了电子计算机、人造卫星和火箭等三个方面的新成就。

The thesis summed up the new achivements made in electronic computers , artificial satellites and rockets.（省略“等三个方面”)

3) 真空管的五大主要职能是：整流、放太、振荡、调制和检波。

The principal functions that may be performed by vacuum tubes are rectification, amplification, oscillation, modulation and detection. (省略“五大”）

4) 电流的主要效应有磁效应、热效应和化学效应三种。 

The chief effects of electric currents are the magnetic, heating, and chemical effects. (省略“三种”）

5) 声音的频率、波长和速度三者是密切相关的。

The frequency, wave length and speed of sound are closely related. (省略“三者”）

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