During a project concerning words in digitized books, researchers estimated a total of 1,022,000 words and they also said that this number would rapidly increase by several thousands in a year!
but, when you see a number like this, you have to keep in mind that these include different forms of the same word and some of these words may be archaic (referred to words that are not in modern day use)
according to the options given, the best answer would be c) 1,000,000