It is______ a sharp knife ______I can use it to cut open a hard pumpkin.[ ]

_____ you try it, you will find it is a joyful sport.[ ]

_____ hours do you exercise every day? [ ]

Look at the boy running on the playground. Is it David? —- It ______ be him. I saw him go to the teachers’ office just now.

The social worker asked Daniel ______________.