现在小明和妹妹还是相差九岁，设小明现在x岁，妹妹y岁。x+y=19x-y=3（x+y）+（x-y）=19+32x=22x=11则y=11-3=8所以小明11岁，妹妹8岁
olescent is the very important time for one life. D
