患者女，45岁。发现左乳腺包块2周，无痛，既往无 * * 溢液史。查体：左乳中央区可触及一

现代科学技术的发展与材料科学、能源的开发密切相关，下列关于材料、能源的说法正确的是[ ]

A.化石能源为清洁能源

B.纳米材料的粒度在1-100μm之间

C.半导体材料的导电性能介于金属导体和绝缘体之间

D.液晶既有液体的流动性，又有光学性质的各向同性

短文改错。

     Mobile phones are being more wide used. They're light in weight and easy to carry, offer fast and

convenient service for communication. The users use them for making phone call, sending short messages

and Internet-surfing. In recently years, mobile phones have become popular to middle school students.

Quite a few use it to keep in touch with their families and friends, what, of course, was of great

convenience. However, I don't think it's good to do so. In spite of the advantages mentioned above, student

users often waste a lot of time chat on the phone in their spare time. Some even cheat in exams. In addition,

mobile phone bills spend their parents lots of money.

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试述车轮的主要故障及防止方法？

食品添加剂改善了人们的生活，但做馒头的过程中禁止添加的是

A．食盐

B．蔗糖

C．小苏打

D．增白剂

计算机教室的所有学生计算机突然都同时不能上网，不可能的原因是（）。

A、该教室的交换机故障

B、提供该教室上网的代理服务器故障或停用

C、学生计算机故障

D、学生计算机网线故障