商品流通的制约因素通过商业环节影响流通渠道，正是商业环节的有与无、多与少，形成了多种商品流通渠道并存的（）。
参考答案：流通渠道体系
Rainforests ____ and burned at such a speed that they will disappear from the earth in the near future.
A．cut
B．are cut
C．are being cut
D．had been cut
一般来说，花卉对气体有指示功能，如（）对二氧化硫很敏感。
A.丁香
B.百日草
C.波斯菊
D.向日葵
