1．Burning coal has led to g________ warming.
2．They will do their best to g________ more energy from the wind and sun.
3．Many great people，such as Sun Yetsen and Mao Zedong，were once active in the south，leaving behind many historical s________.
4．The 20kilometrelong subway is so far Guangzhou’s largest c________ project.
5．Professor Smith is busy doing h________ research.
