Bill Gates (L), co-chair and trustee of Bill and Melinda Gates Foundation, receives an exclusive interview with the Xinhua News Agency during the Boao Forum for Asia (BFA) Annual Conference 2013 in Boao, South China's Hainan Province, April 8, 2013. (Xinhua/Jiang Enyu)

Bill Gates, co-chair and trustee of Bill and Melinda Gates Foundation, receives an exclusive interview with the Xinhua News Agency during the Boao Forum for Asia (BFA) Annual Conference 2013 in Boao, South China's Hainan Province, April 8, 2013. (Xinhua/Jin Liwang)

Bill Gates, co-chair and trustee of Bill and Melinda Gates Foundation, shows a file photo of him as receiving an exclusive interview with the Xinhua News Agency during the Boao Forum for Asia (BFA) Annual Conference 2013 in Boao, South China's Hainan Province, April 8, 2013. The file photo, taken by Xinhua photographer Jiang Enyu, showed Gates delivering a speech at the BFA Annual Conference 2007. (Xinhua/Jiang Enyu)

Bill Gates, co-chair and trustee of Bill and Melinda Gates Foundation, receives an exclusive interview with the Xinhua News Agency during the Boao Forum for Asia (BFA) Annual Conference 2013 in Boao, South China's Hainan Province, April 8, 2013. (Xinhua/Jiang Enyu)

Bill Gates, co-chair and trustee of Bill and Melinda Gates Foundation, receives an exclusive interview with the Xinhua News Agency during the Boao Forum for Asia (BFA) Annual Conference 2013 in Boao, South China's Hainan Province, April 8, 2013. (Xinhua/Jin Liwang)