TWO activists involved in China's pro-democracy movement plan to run for next month's district board polls despite uncertainty over their eligibility. Lau Shan-ching, who spent 10 years in jail for ''counter-revolutionary'' activities, will be joined by Yiu Yung-chin, a former student leader, in campaigning for the district board seats. But their involvement in China's fight for democracy has cast doubt on whether they are eligible candidates. Mr Lau, 41, could be challenged for not having ordinarily resided in Hong Kong for the 10 years immediately preceding the date of his nomination, as is required under the Electoral Provisions Ordinance. He was sentenced in 1981 for ''counter-revolutionary'' activities following a Guangzhou trip to pay visits to participants of the 1979 Democracy Wall movement. Mr Lau was released in December 1991. Despite repeated requests for clarification from the Constitutional Affairs Branch, Mr Lau was told it would be up to the returning officer to confirm his eligibility. He remains adamant that his right to run for election should not be stripped because of his absence from the territory as a result of ''political persecution'' in China. Mr Yiu, 24, was detained in China for a year for his involvement in the 1989 pro-democracy movement. A mainland-born Hong Kong resident, he was a student in Shanghai and a member of the Autonomous Union of Shanghai Universities and Colleges, which was branded as subversive by China in 1989. He was arrested shortly after the Tiananmen Square massacre and released in 1990 with a statement of ''exemption from prosecution''. Electoral laws stipulate a person will be disqualified from seeking election if he has been sentenced in any territory to imprisonment for a term exceeding three months in the past 10 years.