A little boy wrote _____ “u” and _____“n” on the wall.
Can a plane fly _____ the Atlantic Ocean?—Yes, but it needs to go _____ the clouds for hours. [ ]
Where was your father when I called you, Tony?— He ____________ his car.
There are ______visitors in Hangzhou every year.
The box is ________ heavy ________ I can’t lift it.