The first proposal for this new research vehicle, the X-15, was made in nineteen fifty-four.

VOA: special.2010.07.07

This is now on the heap it's four bytes so what gets stored in X?

在堆上，它是4个字节,那么在x中存储的是什么？

哈佛公开课 - 计算机科学课程节选

The company took less than four years to produce three X-15s.

VOA: special.2010.07.07

The X-15 project had four major goals.

VOA: special.2010.07.07

The Vatican has said that before members of the traditionalist Society of St Pius X, like the four bishops whose excommunication was lifted, can be fully readmitted into the Church it must accept the teachings of the 1962-1965 Second Vatican Council which urged respect for other religions.

VOA: standard.2009.03.12