If ∑anxn\sum a_n x^n∑anxn has radius R=1R=1R=1 and ∑bnxn\sum b_n x^n∑bnxn has radius R=3R=3R=3, what is the radius of convergence of ∑anbnxn\sum a_n b_n x^n∑anbnxn?
111
333
444
999