Russia and China's relationship with America affecting Iran's nuclear case

In Iran's nuclear case, there are China and Russia who play very significant role. In spite of West's prohibitions against Iran, these two countries stood against the severe menaces approved by UN Security Council. Elected with the slogan of change, Obama, unlike Bush, so as to open the relation with Russia, laid aside the most important challenging issue which led to rocket shield in the Eastern Europe. Previously defending from Iran's nuclear case, in order to get concession from America, Russia, once getting a bigger carrot, did exactly as America did in boycotting Iran and that is its not giving Iran the s-300 rocket. It is in such a case that China's relation with America not only got better but also, in some parts, became more strained. This time, more then ever, China apposed against the prohibitions, however, it is to say that, China's policy is to have no challenge with America and, so, though being apposed to Iran's boycott, has no chose but get to the site of America.