A：雪地车轮上安装较宽的履带
B：切蛋器装有很细的钢丝
C：打孔机上安装很尖的钻头
D：剪刀刃做的很薄
函数fx=sin2x-π4x∈R的单调递增区间是____
12+1 = 2−1 ， 13+2 = 3−2 ， 14+3 = 4−3 ， 15+4 = 5−4 ，…
解答下面的问题：
A single-parent child should have the right to enjoy normal parental love from both just as his other peers, which some psychologists see as _____to their emotional well-being.
下面有关安全用电的几种说法中正确的是（ ）
