What is the greatest positive integer x such that 7^x is a factor of 343^10?\nOptions:\n(A) 5\n(B) 9\n(C) 10\n(D) 20\n(E) 30
Use reasoning to answer the following question.
(E)
343^10 = (7^3)^10 = 7^30.

The answer: (E)