问题
                    
e ________ extreme caution in ________ use of this medicine, which has not been officially approved yet.
                            A:an; the
B:an; 不填
C:不填; the
D:不填; 不填;
                        
                        B:an; 不填
C:不填; the
D:不填; 不填;
正确答案是:
                        