It is generally believed that teaching is _____ it is a science[ ]

Were you at home at 8:00 last night I called you but nobody answered.— Sorry, I a nap at that time.

homework ,the children also have to take arts, music and sports classes intheir free time.— I wonder what they will become.

John has put forward _______ most challenging question for us to answer.-Yes, it really is. I have never heard _______ harder one.

Thousands of fans waited in the rain for the pop star to arrive. [ ]