语法与词汇 5.Traditionally people believed that obesity resulted from overeating only. Today, however, many doctors believe that it is a (n) ______of genes.
【正确答案】 B
【答案解析】本题考查名词辨析。It's a matter of sth．是固定句型，意为“这是……的问题”，故答案为[B]项。