皮肤角质层厚，皮肤（）。
A.红润
B.有光泽
C.吸收能力强
D.发黄
参考答案：D
.
By around 900 AD,there were many places in Northern Europe______the Vikings chose to live.
A．in which
B．when
C．which
D．at which
如图1所示，试画出光源S发出的一条光线经平面镜反射后通过A点的光路图． 如图2所示，画出入射光线AO的折射光线.
