No one knows ______ the task will last. What a pity!

 In our life, we can work hard on one task 　　　, and then another. In this way, all your dreams can be realized.

Which is _____ difficult, this one or the other two?

I haven’t had enough _______recently, so I’m always _______all day.

—Who’s that boy?—He is my cousin, and _______ name is Jack.