题干
"Tom, ______ rubbish into the river. You're polluting it," said Mrs White.
A：not throw
B：don't throw
C：not to throw
D：never to throw
答案(点此获取答案解析）
B
"Tom, ______ rubbish into the river. You're polluting it," said Mrs White.
A：not throw
B：don't throw
C：not to throw
D：never to throw
、
、……
的平均值为
，方差为
，则
，
，…… 
的平均值和方差分别为（ ）