A:防洪和利于航运
B:开垦两岸的沙洲
C:修建灌溉工程
D:开发河流的水能
已知A={﹣4,2a﹣1,a2},B={a﹣5,1﹣a,9},且A∩B={9},则a的值是( )
Mr. Smith gave the tickets to all the students except _______ who had already seen the movie.