指出改变图层选取颜色的目的？
参考答案：
图层选取颜色，决定节点和方向线在图层中显示颜色，易于识别。
用所给单词的适当形式填空.
1. Christmas Day is on December _____ (twenty-five).
2. A week _____ (late), the man came again.
3. Look! They _____ (decorate) their Christmas tree.
4. Christmas is an important holiday in _____ (west) countries.
5. Let's _____ (not sit) on the chairs.
呼吸衰竭的病因没有下面哪项：（）
A.胸廓畸形
B.气管异物
C.广泛肺炎
D.腹水、腹内压升高
E.氰化物中毒
