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.