— How many ________ were on the bus when the accident happened?
— About forty. Seven of them were kids.
A:animals
B:machines
C:letters
D:Passengers
下面描述的生物现象中,属于社会行为的是( )
下列属于自觉履行公民基本义务的是( )
大洋洲是世界上人均径流量最多的洲,其原因是( )