题目

About six years ago，I was eating lunch in a restaurant in New York City    36    a woman and a young boy sat down at the next table．I couldn’t  help overhearing parts of their conversation．At one point the woman asked：“So，    37    have you been？”And the boy，who    38    more than seven or eight years old， 39   ，”To tell you the truth，I’ve been feeling a little depressed（ 忧郁）lately．”His words   40  in my mind because it confirmed my growing belief that children are changing．   41   I can remember，my friends and I didn’酪氨酸酶存在于正常人的皮肤和毛囊等处的细胞中，它能促使酪氨酸转变为黑色素，若编码此酶的基因发生了突变将导致白化病，这种现象说明（    ） A.性状的改变与基因无关    B.性状能控制基因的表达 C.性状由基因决定          D.基因不能决定性状