New words：

protein ['prəuti:n] n. 蛋白质
calcium ['kælsiəm] n. 钙

Sample Sentences：

Fish was a major source of protein for the working man.
Try to balance your diet by eating more fruit and less protein.
Milk products are an excellent source of calcium and protein.
It helps your bodies use calcium, which is necessary to keep your bones strong.

source [sɔ:s] n. 来源；源头；根源；原因

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