Article 28 of the Patent Law stipulates that the date when the patent administrative department of the State Council receives the patent application documents shall be the filing date. If the application documents are mailed, the postmark date of mailing shall be the application date.
Paragraph 1 of Article 42 of the Patent Law stipulates that the term of an invention patent is 20 years, that of a utility model patent is 10 year, and that of a design patent is 15 year, all of which are counted from the date of filing.
Therefore, the protection period of a patent should be calculated from the actual application date, not from the priority date. In this topic, the patent of an American company is an invention patent and the protection period should be 20 years; The actual filing date of China is May 9, 2005, so the protection period should be counted from that date. The author's answer to this question is item B.