若方程x2﹣2x﹣3=0的两个实数根为x1，x2，则x1+x2= _________ ．
2
in her best skirt, the girl tried to make herself at the party.
A．Dressed; noticed
B．Dressing; noticing
C．Dressing; noticed
D．Dressed; noticing
对被粘物表面进行打磨处理，能提高粘接强度和牢度，为什么？
