2 . It is difficult to forecast ___________ threats our heritage sites will face in the future, but we have the belief that we will need this kind of cooperation in heritage preservation. (用适当的词填空)

4 . When he got older, John started to wonder ________ this process could be used to clean up the messes people were making. (用适当的词填空)

6 . Interestingly, the calligrapher Wang Xizhi from the Eastern Jin Dynasty wrote in his Lanting Xu about _________ literary men composed poetry while drinking from cups left floating and moving along the winding river. (用适当的词填空)

9 . Now carrying a strong cultural legacy of past human activity, the woodland has become a quiet monument to _________ we’ve lost in the development of civilization. (用适当的词填空)