“种瓜得瓜，种豆得豆”，这句话描述了生物的____现象．
已知弦AB的长等于⊙O的半径，弦AB所对的圆心角是 ____
下列物理量的估测最接近实际的是（ ）
人体免疫有三道防线,在这三道防线中,属于非特异性免疫的是 ( )
Mr. Chen is very _________ every day. He has no time to help his daughter with her homework.
