Our current CDs and DVDs store data along a narrow spiral track in a thin layer of polycarbonate plastic.

我们现在的CD和DVD沿着一个狭窄的螺旋轨道把数据储存在一个微笑的塑料里。

youdao

The back of the patella is lined with a thin layer of cartilage known articular cartilage. This layer helps the patella track up and down along the front of the femur.

髌骨的背侧有一层薄薄的关节软骨，有助于髌骨沿着股骨前侧进行向上与向下的移动。

youdao

Because the feet are on one 'track' instead of two, thus creating a better body line with partner. (The 'thin' look rather than the 'wide' look)

因为两只脚在同一条线上，而不是在两条线上，这样就能与舞伴展示更好的身体线条。（看起来比较“薄”而不会很“宽”）

youdao

Reilly thinks the ETF is a disaster for the investors picking up the tab because it buys futures in a bid to track a thin underlying market.

FORBES: How To Avoid ETF Pitfalls