农产品的运输是连接商品与销售之间的桥梁。也是（）中的不可缺少的环节
参考答案：商品流通
If they had known what was coming next, they _____ their mind. [ ]
A. may change
B. could change
C. must have changed
D. might have changed
在天线增益一定的情况下，天线的水平半功率角与垂直半功率角的关系为（）.
A、反比
B、正比
C、不确定
D、没有关系
