A:济南、徐州、杭州
B:成都、重庆、南宁
C:武汉、哈尔滨、包头
D:西安、太原、石家庄
2+____=9 ____+6= 6
____-3 =5 ____+____=7
Many a student __________ wearing MP3 players while walking on the street. It's quite dangerous. ( )