以下茎叶图记录了甲组3名同学寒假假期中去图书馆A学习的次数和乙组4名同学寒假假期中去图书馆B学习的次数．乙组记录中有一个数据模糊，无法确认，在图中以x表示．

（1）如果x=7，求乙组同学去图书馆学***均数和方差；

（2）如果x=9，从学***于8的学生中选两名同学，求选出的两名同学恰好分别在两个图书馆学习且学习的次数和大于20的概率．

按要求转换句子,每空一词。
____ It's windy in Beijing. (对划线部分提问)  
______  ______ the weather in Beijing?
____ Mary is talking on the phone.(改为否定句)
Mary _______  _________ on the phone.
____ We're cleaning the playground. （改为一般问句 ）
______  _______ cleaning the playground?
____ My parents are talking with Mr.Green.   (改为一般问句 )
_________ ________ parents _______ with Mr.Green ?
____ A koala comes from Australia. (变否定句)
A koala ________  ________ from Australia.
____ He likes dolphins very much.   (变一般疑问句)
________ he _________ dolphins very much?
____ I like Tom because he is very friendly.  (对划线部分提问)
_________ do ________ like Tom?
____ Pandas are from China.   (同义句转换) 
Pandas _______  ________ China.
____ She likes dumplings, fish and apple juice.(改为否定句)
She ________like dumplings, fish ______ apple juice.
____ She'd like beef and onion noodles for lunch. (就划线部分提问)
_______   _____  _______ noodles ______ she like for lunch?