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.