combine的名词形式

　　An alloy is a combination of two or more different metals.

　　合金是两种以上不同金属结合而成的`。

　　A combination of internal and external factors caused the company to close down.

　　内外因结合导致了公司的倒闭。

　　The two players together make a formidable combination.

　　这两个队员配对儿，难以对付。

　　She brings to the job a rare combination of youth and experience.

　　她很年轻，然而干这份工作已有经验，这是很难得的。

　　This combination of qualities is generally supposed to be extremely rare.

　　一般认为，同时具有这样一些品质极为罕见。