影响轴向窜动的原因有哪些？
参考答案：
装配个别零件尺寸不对，叶轮偏左或偏右。运行中零件磨损，造成个别部件间隙加大而产生轴向窜动。
设命题p：函数f（x）=（a+2）x是R上的增函数，命题q：方程x2+2x+a=0有解，若“p且q”为假命题，“p或q”为真命题，求实数a的取值范围．
--- What were you doing this time yesterday?
--- I ______ on the grass and drawing a picture.
A．sit
B．sat
C．am sitting
D．was sitting
