I have to go after Steve Mercer, she thought for probably the billionth time.

我一定要去找史蒂夫·默瑟，这大概是她第十亿次这样想了。

A nanometre is a billionth of a metre.

十亿分之一米是一纳米。

A nanosecond is one-billionth of a second.

1纳秒为十亿分之一秒。

A nucleus is about one billionth the size of an atom.

原子核的体积大约是原子的一万亿分之一。

In February 2010, the ten-billionth song was sold on iTunes.

2010年2月，iTunes出售的歌曲已经达到了100亿首。