已知a为常数,函数f(x)=x(lnx﹣ax)有两个极值点x1,x2(x1<x2)( )
A:f(x1)>0,f(x2)>-12
B:f(x1)<0,f(x2)<-12
C:f(x1)>0,f(x2)<-12
D:f(x1)<0,f(x2)>-12
下面能说明“液体可以传播声音”的事例是( )
My sister ____ (be) a singer since she left the school.
按要求写单词。
home(近义词)____ mother(同义词)____ table(近义词)____ father(同义词)____
① ____ A. season B summer C. spring
② ____ A. leaf B paint C snowman
③ ____ A because B. but C. hot
④ ____ A. green B tree C. flower