4a2-12ab+9b2-c2.
原式=(4a2-12ab+9b2)-c2
=(2a-3b)2-c2
=(2a-3b+c)(2a-3b-c).
I will be surprised if you can get Calvin, who is very busy, ______these tickets for you.
A.buy
B.buying
C.buys
D.to buy
()工艺主要用于中碳钢及低、中碳合金结构钢的锻件、铸件等。
A.扩散退火
B.完全退火
C.球化退火
D.去应力退火