单项选择题
A．never cause trees injury B．damage trees on purple C．do some harm to trees without knowing it D．not be aware of which trees are healthy
A．Construction of buildings is good for trees. B．Some trees' trouble comes from human beings. C．People should keep trees beautiful. D．Trees are not disturbed by changes around them.
A．that people should protect trees B．that people should plant more trees C．what trees can be used for D．what kinds of trees look beautiful