（）电压等级运行的线路，通过变压器电磁回路的连接而构成的环路，叫做电磁环网。

A.相同

B.不同

C.可能相同

D.其他三个选项都不是

阅读理解。

     Apple trees may grow as tall as 12 metres and they grow best in areas that have cold winters. Although no

fruit is yielded during the winter, this cold period is good for the tree.

The underlined word " yielded" most probably means _____.

A. sold

B. bought

C. improved

D. produced