food and vegetables         southern China where people have being suffered from snow storms since mid-January.

A．Large quantities of; are sent to

B．A large quantity of; are sent to

C．Plenty of; is sent to

D．A great deal of; are sent to

下列哪些因素可以影响示范的有效性？（）

A.示范的场合

B.示范者的身份

C.示范的准确性

D.示范的时机