He is understudying the famous film star .

他在为那位著名影星充当替角。

Understudying ingrid was guaranteed unemployment .

为英格丽当替角是注定要失业的。

But carbon fiber , which is used only sparingly now because of its cost and complexity , is understudying for a larger role .

由于碳纤维的高成本和复杂性，因此宝马对它的使用还比较谨慎，但它未来必然会在宝马汽车上扮演更大的角色。