A:What are you going to stay in Beijing?
B:How long are you going to stay in Beijing?
C:When are you going to stay in Beijing?
Sn是等差数列{an}的前n项和,若S5=20,则a2+a3+a4=( )
读图,出现图中1946—1953年所示现象的原因包括①日本实行“统制经济体制”②二战后美国积极扶植日本③日本实行政府主导型市场经济④日本建立了完善的社会保障制度
青少年偏食,挑食常导致一些疾病的发生,下列疾病与病因对应错误的是( )