问题 选择题
设函数f(x)=
-x,x≤0
x2,x>0
,若f(a)=4,则实数a=(  )
A.-4或-2B.-4或2C.-2或4D.-2或2
答案

当a≤0时

若f(a)=4,则-a=4,解得a=-4

当a>0时

若f(a)=4,则a2=4,解得a=2或a=-2(舍去)

故实数a=-4或a=2

故选B

改错题

短文改错

     Today is Sunday. The sky is full of sunshine, so does my life.                                    1._________

At about 9:00 am, I go to the bookstore with my friends,                                              2._________

there was a lot of new books, but I didn't know which one to buy,                                3._________

because these books were all useful to me. At last, I chose two.                                   

At 10:00 am, we went to the cinema, the film calling Titanic was very                            4. _________

popular. It took us about 3 hours to see. Having seen the film,                                      5. __________

and  everyone was deeply moved. Some friends even burst                                          6. __________

out tears. From the story, I understand that love is noble and valuable.                          7. __________     

That's a real wonderful film. It is very worth seeing again.                                              8. __________

                                                                                                                                   9. __________

What a happy day! I hope tomorrow I will be even happy!                                          10. _________

选择题