若$m<n<0$，则$\left\{\begin{array}{c}x>2m\\ x>-2n\\ x<2n\end{array}\right.$的解集为____ ．

    Betty started to learn English at the____of six. She went to an after-school English class every week. But Betty thought it was____(bored) to go to her English classes. She didn't think____was important to learn English and she did not need to speak English in her everyday life.

    After she____a school baseball team , she started to know more about the baseball players who joined teams in the USA. Now, she wants to know more about what happens to them. So she reads English newspaper____the Internet. When she meets new words, she looks____up in her dictionary and writes difficult sentences in her notebooks. When she goes to school, she asks her English teacher for____. Little by little, she finds that English is really important, and she is more and more____(interesting) in it.

    Her parents promise to take her to New York to watch a baseball game if she gets good mark in the English exam next month.____exciting it is! Betty is so happy that she works____(hard) on English than before.

如图所示，一个变压器原副线圈的匝数比为3∶1，原线圈两端与平行导轨相接，今把原线圈的导轨置于垂直纸面向里、磁感应强度为B=2T的匀强磁场中，并在导轨上垂直放一根长为L=30cm的导线ab，当导线以速度v=5m/s做切割磁感线的匀速运动时（平动），副线圈cd两端的电压为____ V。

⑴两条直线a，b没有公共点，那么a与b是异面直线．

⑵如果直线a，b和平面α满足a∥平面α，b∥平面α，那么a∥b．

⑶如果直线a，b和平面α满足a∥b，a∥平面α，那么b∥平面α．

⑷若直线a不平行于平面α，则平面α内不存在与直线a平行的直线．

⑸如果直线a∥平面α，点P∈平面α，那么过点P且平行于直线a的直线只有一条，且在平面α内．

果树结果太多，会影响果实的大小和质量，常用喷洒生长素类似物的方法进行疏花疏果，其原理是（　　）