Unquestionably, the answer is (C) - produzcan. The present subjunctive is needed here in the 3rd person plural to match "muchos países". The subjunctive is needed because there are (1) two different subjects (2) two different clauses - a main clause and a dependent clause (starting with "que"), and (3) expression of doubt in the main clause -- No pienso...
"No pensar" and "No creer" may seem not to fit what one would deem a need for subjunctive in the main clause but BOTH these verbs, when expressed in the negative form, do, in fact require the subjunctive, as long as there are two different subjects and two different clauses, as I explained above.
Rita C. Silvia
B.A. Spanish, University of Massachusetts-Boston
M.Ed. Cambridge College Cambridge, Mass.
20+ years experience as a high-school and adult teacher of Spanish