A【3】patent is the result of a bargain【4】between an inventor and the state, hut the inventor gets a limited period of monopoly and publishes full details of his invention to the public after that period【5】.
Only in the most exceptional circumstances【6】the lifespan of a patent【7】to alter this normal process of events.
The longest extension ever【8】was to Georges Valensi; his 1939 patent for color TV receiver circuit was extended until 1971 because for most of the patent's normal life there was no color TV to【9】and thus no hope for reward for the invention.
Because a patent remains permanently【10】after it has terminated, the shelves of the library attached to the【11】office contain details of literally millions of ideas that are free for anyone to use and, if【12】than half a century, sometimes even repatent. Indeed, patent experts often advise anyone【13】to avoid the high cost of conducting a search through【14】patents that the one sure way of violation of any other inventor's right is to plagiarize a dead patent. Likewise, because publication of an idea in any other form【15】invalidates further patents on that idea, it is traditionally【16】to take ideas from other areas of print. Much modern technological advance is【17】on these presumptions of legal security.
Anyone closely【8】in patents and inventions soon learns that most "new" ideas are, in fact, as old as the hills. It is theft reduction to commercial practice, either through necessity or dedication, or through the availability of new technology,【19】makes news and money. The basic patent for the theory for magnetic recording dates back to 1886. Many of the original ideas behind television originate【20】the late 19th and early 20th century. Even the Volkswagen rear engine ear was anticipated by a 1904 patent for a cart with the horse at the rear.
(1)

A. work
B. possibility
C. measures
D. courses