其它组分含量不超过规定限量的气体是（）气体
A.特种气体
B.单一气体
C.混合气体
参考答案：B
认股权证持有人，在认股之前，既不拥有债权也不拥有股权，只拥有股票认购权。 ( )
David ________ from the analysis of the traffic accident that it had been caused by human error.[ ]
A．announced
B．acknowledged
C．concluded
D．considered
