设，其中a2+c2≠0，则必有（）。 A.b=4d B.b=-4d C.a=4c D

一盒钢笔有12支，每支钢笔的售价是8元．15盒这样的钢笔售价是多少元？

用所给动词的适当形式填空。

1  He _____ (wash) the dishes in the kitchen when I saw him yesterday evening.

2. Some old people are happy _____ (be) with the young ones.

3. Tom says he _____ (not watch) the video film tonight.

4. How _____ Bob _____  (go) to school every day except weekends?

5. "Mun, I saw a new kind of bike. It _____ (cost) only two hundred and fifty yuan,"  "Oh, really?"

6. Can she _____ (run) as fast as Helen ?

7. We_____ (visit) the Great Wall next week.

8. Don't _____ (talk) now.

9. Let's_____ (try) our best _____ (finish) the work in an hour.

仪表的精度是根据仪表的（）来划分的。

A．绝对误差

B．相对误差

C．引用误差

D.系统误差

原发性三叉神经痛的患者可能出现的体征（）。

A.患侧面部感觉减退

B.患侧咀嚼肌萎缩

C.患侧角膜反射消失

D.患侧面部可有触发点

E.张口时下颌偏向患侧

说明门机台车轮啃轨的原因及排除方法。