无内胎轮胎近年来应用日益广泛，它没有内胎和垫带，空气直接压入外胎中，其密封性是由外胎和轮辋来保证的。
参考答案：对
制作PFM全冠时，金属基底表面氧化膜厚度最佳值为（）
A.0.2～2μm
B.5～10μm
C.15～20μm
D.25～30μm
E.30μm以上
根据句意及首字母提示，写出单词。
1. There are many people in the supermarket. It's too c ____
2. Traveling by train is the most c ____ way.
3. Lucy lives f_____ from school, so she has to go to school by bus.
4. It's the best way to g____ to school by bike.
5.M ___ than 50 teachers will come here tomorrow.
