A: Can he swim?
B: ____
A: What can he do?
We are glad to hear that the terrorists ________ by the brave policemen several days ago.
若将绿藻甲、乙、丙、丁四组分别放置于:湖泊、100m深的海中、800m深的海中,50m深的海中,首先死亡的是生活在何处的绿藻?( )
209506精确到千位的近似值是____.