熔化合金的方法中,以哪种方法达到的温度最高()
A.汽油空气吹管
B.煤气-空气吹管
C.乙炔-氧气吹管
D.高频感应铸造机
E.碳棒电弧熔金
参考答案:C
下列运算中,正确的是[ ]
A.(x﹣y)(﹣x+y)=x2﹣y2
B.(﹣x+y)(﹣x﹣y)=﹣x2﹣y2
C.(2x+y)(2x﹣y)=2x2﹣y2
D.(﹣2x﹣y)(y﹣2x)=4x2﹣y2
用所给单词的适当形式填空。
1. Where's the (体育用品商店)?
2. These clothes are fifty (美元)
3. Lynn doesn't have (一些) homework to do.
4. She wants to buy a pair of (跑鞋).
5. He is (学着打篮球) now.