不但能够防止丢失修改，还可进一步防止读脏数据，但不能防止不可重复读的封锁协议是（）。

A.一级封锁协议

B.二级封锁协议

C. 三级封锁协议

D.四级封锁协议

句型转换(由直接引语变间接引语/由间接引语变直接引语)。

1.The teacher asked me，“Do you have difficulty working it out?”______________________________________________________________________________________________________________________________________________________________

2. His father said to him，“I will have a picnic tomorrow. ”______________________________________________________________________________________________________________________________________________________________

3. Tom asked Kate，“How did you get the book?”______________________________________________________________________________________________________________________________________________________________

4. Mike told Kate not to play with water.______________________________________________________________________________________________________________________________________________________________

5. Lucy said to Jim she had finished the homework two hours before.______________________________________________________________________________________________________________________________________________________________