The first plane ever to fly faster than the speed of sound was the X-1 in nineteen forty-seven.

VOA: special.2010.07.07

The X-15 was the first major investment by the United States in manned space flight technology.

VOA: special.2010.07.07

In the memorial, there is the X-1, the first airplane to fly faster than sound.

VOA: special.2010.07.07

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

VOA: special.2010.07.07

But the U.S.Preventive Services Task Force advised women in their 40s to delay their first mammogram until age 50,and after 50, schedule the x-ray every other year.

VOA: standard.2009.12.25