A:身体分为头、胸腹
B:有三对足
C:体表湿润,完成呼吸
D:有两对翅
For our safety, we'd better avoid ____ (go) out alone at night.
儿童青少年心理健康的核心是( )
已知向量a→=(2,1),b→=(x,﹣1),且a→﹣b→与b→共线,则x的值为____