beef是可数名词还是不可数名词

　　The smell of roast beef permeated the air.

　　烤牛肉的气味弥漫在空气中。

　　Japan is the biggest importer of U.S. beef.

　　日本是美国牛肉的最大进口国。

　　Thick tuna steaks are eaten rare, like beef.

　　厚厚的金枪鱼片要半熟吃，就像牛肉一样。