A:①
B:①②
C:①②③
D:①②③④
My house is close ______ the Queen's house. ( )
设Sn是等差数列{an}的前n项和,若 S3S6 = 13 ,则 S6S12 =( )
You had better learn to _________ different kinds of problems by yourself.
常见金属活动性顺序如图4:下列各组物质间能发生反应的是