血栓闭塞性脉管炎早期的典型症状是()
A.肢端发绀,发凉
B.间歇性跛行
C.肢端干性坏疽
D.下肢肌肉萎缩
E.持续性疼痛
参考答案:B
某物体运动中沿x、y互相垂直方向的分运动的速度图象如图所示,求经过多长时间速度大小为50m/s,此时速度方向如何?
In the Oral Approach language teaching begins with the spoken language. Material is taught orally before it is presented in the ______ form.