Many _______ of years later, the first extremely small plants began to appear on the surface of the water.
Is this the factory______ he worked ten years ago?
______ entering the room, she opened her bag to review lessons.
This is the reason ______he explained at the meeting for his carelessness in his work.
______ is a waste of time spending many hours ______ computer games every day.
He is a man of great experience ______ we can learn a lot.