单项选择题
A. Two passenger trains collided head-on. B. A passenger train killed 14 people. C. A passenger train went off its track. D. A passenger train was trapped inside the station.
A. its trade in sensitive nuclear materials. B. its nuclear test. C. its nuclear and missile program. D. its nuclear energy program.
A. maintain balance and improve coordination. B. protect brain cells from damage. C. increase the brain’s memory storage capacity. D. keep brain alert.