19.
A. Piracy is an easy thing to commit.
B. Invention usually needs heavy cost.
C. Patent is useful but not practical.
D. Inventions are difficult to spread.
20.
A. Solve the conflicts privately with the inventor.
B. Give the inventor some compensation.
C. Buy the patent from the real inventor.
D. Give all the fake commodities to the inventor.
21.
A. The inventor decides who the expired patent goes to.
B. The inventor may strive for a longer valid time span.
C. The inventor will try hard to sell his products faster.
D. The inventor will hesitate when giving his data to the public.

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