arm and leg：胳膊和腿。

an arm and a leg：大价钱，巨额花费。

The boy fell from a tree and suffered fractures of his right arm and leg.

这个男孩从树上摔了下来，使右手和右腿骨折了。

These shoes cost me an arm and a leg.

这些鞋子花了我好多好多钱。