树脂片有何缺点?
参考答案:
镜片耐膜性较差,易摔碎,折射率低,相对比玻璃片要后1.2——1.3倍
用特殊疑问词填空。
1. — ______ did he go?
— By plane.
2. — ______ did you live at the time?
— At No.3, Beijing Road.
3. — ______ is your telephone number?
—It's 3065431.
4. — ______ were you then?
—I was twenty-six.
5. — ______ car is yours?
—The blue one.
6. — ______ is it from here to your house?
— About two miles.
7. — ______ was it yesterday?
—It was Tuesday.
8. — ______ students are there in the classroom'?
下列梁桥结构中,支座上的卸载弯矩为零的是()。
A.悬臂梁
B.固端梁
C.连续梁
D.简支梁