多选题Given two collection objects referenced by col1 and col2，which of these statements are true？（）AThe operation col1.retainAll（col2） will not modify the col1 object.BThe operation col1.removeAll（col2） will not modify the col2 object.CThe operation col1.addAll（col2） will return a new collection object， containing elements from both col1 and col2.DThe operation col1.containsAll（Col2） will not modify the col1 object.
多选题
Given two collection objects referenced by col1 and col2，which of these statements are true？（）
A
The operation col1.retainAll（col2） will not modify the col1 object.
B
The operation col1.removeAll（col2） will not modify the col2 object.
C
The operation col1.addAll（col2） will return a new collection object， containing elements from both col1 and col2.
D
The operation col1.containsAll（Col2） will not modify the col1 object.
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