农产品的最终销售多为零售，需求弹性较低，决定了农产品广告的（   ） 特点。
The final sales of agricultural products are mostly retail, and the demand elasticity is low, which determines the (   ) characteristics of agricultural product advertising.  A.
季节性
seasonal  B.
广告效果测定困难
difficulty of advertising effect measurement C.
广告费用不宜过高
low cost of advertising  D.
调节控制性
 regulatory control