bananas are usually sold by ____weight,and eggs are sold by _______(a ,an ,the填空）

bananas are usually sold by ____weight,and eggs are sold by _______(a ,an ,the填空）

bananas are usually sold by weight,and eggs are sold by the dozen.
香蕉通常是按重量来卖的,鸡蛋是按打卖的.
by 后面跟名词是不用加任何定冠词的
但是后面跟量词就要加the,比如kg 就要用by the kg

不填
the dozen

不填， the dozen（打）

不填
the dozen