下面有几段文章,每一个段落均需要一个句子表达其中心思想,这个句子就是主题句。你应很快地从三个供选择的答案中挑选出适宜的主题句来。 Paragraph 1 Complete proteins,which the body needs for growth,have all the essential amino acids; meat,fish,poultry,eggs,milk,and cheese,have complete proteins. The body needs complete proteins everyday. The second kind,incomplete proteins,do not have all the essential amino acids. The proteins in vegetables and grains,for instance,are incomplete proteins. Two ways to form complete proteins from incomplete proteins are: ( 1) to mix vegetables and grains correctly,or ( 2) to add a small amount of meat or milk to a large amount of grains. The body can then use the complete proteins which result from the mixtures.