在一个透明的布袋中，红色、黑色、白色的玻璃球共有80个，它们除颜色外其他完全相同，小李通过多次摸球试验后，发现其中摸到红色球、黑色球的频率分别为15%和45%，则口袋中白色球的数目很可能是　 ____　个．

乐乐为探究新制饱和氯水成分做了如下实验，他根据实验现象得出的结论不正确的是（　　）

如图所示，已知m_A=2m_B=3m_c，它们距轴的关系是r_A=r_C= $\frac{1}{2}$ r_B，三物体与转盘表面的动摩擦因数相同，当转盘的速度逐渐增大时（   ）

    Do you know Stephen Hawking? He's one of the most well-known____（scientist）on space and time in the world. He was born in England in 1942. Hawking is ____（study）how the universe began and how it ends.

    When he studied math and science at Oxford University, he fell____(serious) ill, which made him unable to speak or breathe. Till now, he can't move or feed____(him). however, he has a wheelchair with ____ special computer, with which he can communicate with others.

    ____he was facing all these difficulties, he refused to give up his hope of living. Because____ his illness, it was difficult for him to draw diagrams or to write. So he started____(think) in pictures. With this new way of thinking, he is respected by people in the world.

    Once he____(invite) to China to give lectures. His self-confidence and humorous conversations impressed us deeply.

    He once said, “When something unfair happens,____ is no need to worry about it! You just have to do the best in your own situation.”