问题
                    
24The Niagara Waterfalls, ______ is shaped like a semicircle, are 670meters wide, and fall 56 meters in an awesome white sheet of water
                            A:what
B:where
C:the largest of which
D:in which
                        
                        B:where
C:the largest of which
D:in which
正确答案是:
                        