1)In April, there was the "ping" heard around the world. In July, the ping "ponged".

　　四月里，全世界听到中国“乒”的一声把球打了出去;到了七月，美国“乓”的一声把球打了回来。

　　这句如只译为“四月里，全世界听到乒的一声;七月里，这乓声却乓了一下”，读来就不知所云。

　　2)Nixon learned that Ceausescu would welcome a presidential visit.

　　尼克松了解到，齐奥塞斯库欢迎美国总统访罗。

　　本句上文曾提到美国总统访问罗马尼亚。

　　3)Bundy was not considered to have signed on, and it was known that the President was wavering, that Ball was making his stand.

　　一般认为，邦迪并没有同意轰炸，总统还在犹豫不决，而鲍尔已明确反对轰炸。

　　本句上文中提到的是“轰炸”问题，翻译时根据上下文，补充了“轰炸”和“反对轰炸”，意思就比较清楚。