In April, 1996, Hans Hoff Invented an Invisible Teflon Coating

Multiple Choice

In April, 1996, Hans Hoff invented an invisible Teflon coating for silk that could be used in men's ties so stains would wipe off easily. In May, 1996, Geraint Wynn-Ffolkes independently invented the same coating, and was granted a patent for it. Hans wants to attack the patent. Which of the following is true?

A) There are no grounds to attack a patent. Once it is granted that is final.
B) A patent can be impeached but Hans will not be successful because Geraint registered first.
C) A patent can be impeached and Hans will be successful because he invented the coating first.
D) A patent can be impeached and Hans will be successful because the matter was not the proper subject matter for a patent.
E) It is too late to impeach the patent. Hans should have opposed Geraint's application.