问题
                    
The skin, an ____ part of your body and its largest organ, ____ as a barrier against diseases.[ ]
                            A: vital, acting 
B: vital, acts
C: essential, acting
D: essential, acts
                        
                        B: vital, acts
C: essential, acting
D: essential, acts
正确答案是:
                         
                        
                        
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