A:单质的氧化性按X、Y、Z的顺序增强
B:阴离子的还原性按X、Y、Z的顺序减弱
C:气态氢化物的稳定性按X、Y、Z的顺序增强
D:元素非金属性按X、Y、Z的顺序减弱
如果(x+1)(x2﹣2ax+a2)的乘积中不含x2项,则a=____
设点A(﹣3,5)和B(2,15),在直线l:3x﹣4y+4=0上找一点P,使|PA|+|PB|为最小,则这个最小值为____
make up one's mind; give in; ever since; be fond of; grow up: on schedule; change one's mind ;care about; prefer to; get sb. interested in