护轨下垫板大于20mm时，必须加设铁垫板和加长道钉。
参考答案：错
. 若直线x－2y＋5＝0与直线2x＋my－6＝0互相垂直，则实数m＝______.
—I have a _______.
—You shouldn’t eat too much candy.
A. toothache B. headache C. backache
