Mobile phones are becoming more and more popular not only with____(grown-up) but also with students. Meanwhile,they also____(become) a problem for middle schools in the past few years.Some children have got mobile phones____Christmas or birthday gifts,and more will still want them.

    Many like SMS because it is____(ease) and quick.Some parents felt happy because they could communicate with their children.Some teachers said mobile phone use____(be) a distraction（分心的事）to students during school hours and____also gave them much trouble in their classrooms.Sometimes students might use phone messages____(cheat) during exams.A new study found that some teenagers sending messages in class even hurt their fingers because they can't stop____(send) SMS.

    Many teachers suggested that students should not have phones at school,but if there was a good reason,they could leave their phones at school office.And even they can use the telephone in the teachers' office instead.Many people think they understand the reason____parents would want their children to have them,but they agree schools should tell the students____(use) their mobile phones at proper times.

实验是检验化学原理的“最高法庭”．下列化学实验基本操作中正确的是（　　）

如图，在⊙O中，弦AB⊥AC，OD⊥AB于点D，OE⊥AC于点E，若AB=8cm，AC=6cm，则⊙O的半径OA的长为（　　）