BEIJING (Reuters) - China s foreign ministry said on Monday it had lodged  solemn representations  with the North Korean embassy in Beijing over the North s sixth and most powerful nuclear test. North Korea is clear about China s opposition to its nuclear tests, ministry spokesman Geng Shuang told a regular briefing, adding that China upholds talks as the means to resolve the Korean peninsula issue. The North said it tested an advanced hydrogen bomb for a long-range missile on Sunday, prompting a vow of  massive  military response from the United States if either it or its allies were threatened. 