by the end of the month the estate agent will sell/will have sell/have sold twenty houses.为什么?

by the end of the month the estate agent will sell/will have sell/have sold twenty houses.为什么?
by the end of the month the estate agent will sell/will have sell/have sold twenty houses.为什么?

by the end of the month the estate agent will sell/will have sell/have sold twenty houses.为什么?
到月底,楼盘售房处将销售20栋房子

have sold- past tense

用将来时态~
by the end of month表达的意思是“（预计）到月底”~~