如图，边长为6的大正方形中有两个小正方形，若两个小正方形的面积分别为S₁、S₂，则S₁+S₂的值为（　　）

已知集合A、B、C且A={直线}，B={平面}，C=A∪B，若  a∈A，b∈B，c∈C，有四个命题①$\left.\begin{array}{c}a\mathit{\parallel }b\\ c\mathit{\parallel }b\end{array}\right\}\Rightarrow a\mathit{\parallel }c$②$\left.\begin{array}{c}a\perp b\\ c\perp b\end{array}\right\}\Rightarrow a\mathit{\parallel }c$③$\left.\begin{array}{c}a\mathit{\parallel }b\\ c\perp b\end{array}\right\}\Rightarrow a\perp c$④$\left.\begin{array}{c}a\perp b\\ c\mathit{\parallel }b\end{array}\right\}\Rightarrow a\perp c$其中所有正确命题的序号是（ ）

下列句子中划线词语能被括号中的词语替换且不改变句意的一项是（      ）。

    Christina is an American girl. She is a good student. Every morning she gets up at 6:00. She has her breakfast at home. Then she wears her uniform and goes to school. She studies hard every day. She eats in the dining room when she is in school. After school, she does her homework first, then she cleans the room and helps her mother with the dinner. Before she goes to bed, she usually reads some books. Then at 10:00 p. m. she goes to bed. She thinks she is happy every day. What do you think of her?

春节一过，不少媒体报道了沿海发达地区遭遇“用工荒”的情况，同样，内地各大城市遇到“用工荒”倒春寒袭击。“用工荒”对劳动者的积极意义在于（   ）