A．The cost of making paper.
B．Large machines and paper-making.
C．The development of paper-making.
D．How to make paper by hand today.
A．The continents and ocean floors move violently.
B．The earth is as permanent as it was.
C．The surface of our planet is always in motion.
D．The crust of the earth moves frequently.
A．It shows the structure of the earth.
B．It leads to new changes.
C．It may not be true.
D．It is an important revolution in scientific thought.