text:  China, calling on scientists from around the world to join them in studying, recently obtained samples from the moon. Senior Chinese space official Bian Zegang confirms the calls gone out for experts around the world to come and help examine the rocks from the far side of the moon, with one exception, the U.S. The problem, he says, is the 2011 Wolf Amendment, which prevents direct U.S.-Chinese bilateral cooperation, which in this case hampers such exchanges.