用公式法解方程x2-5x+6=0,则方程的根是______.
x2-5x+6=0
x=5±25-242
x=3或x=2
故本题的答案是x1=3,x2=2.
Pleasant music is often played ________ classes to make students refreshed and relaxed for a while.
A.after
B.between
C.among
D.over
关于呼吸阀的作用,下列说法错误的是()
A、自动控制油罐气体通道的启闭
B、对油罐起到超压保护作用
C、减少油品蒸发损耗
D、阻止空气的进入