The teacher knows that you are always the first ________ to the classroom since last september.

 Charles Babbage is generally considered ______ the first computer.

More than a quarter of the energy       in the United States goes to moving people and goods from one place to another.

Since then, more than 2 billion apps have been downloaded at prices ________ free to $900. 

Each of the students，working hard at his or her lessons，         to go to university.