I have been told many different things about the correct placement of the agent. I learned that in passive voice the agent can be omitted or added at the end of the sentence.
The research team has been studying the new species for a month =
The new species has been studied for a month by the research team.
However, is it more or equally correct to place the agent in the middle of the sentence?
The new species has been studied by the research team for a month.
Which one is more common? Is there a grammatical reason to put it in one place or another?
Also, can the agent be placed anywhere in the sentence?
The new species, by the research team, has been studied for a month.
By the research team, the new species has been studied for a month.
The new species has by the research team been studied for a month.
Maybe it is akward to a native speaker but is it possible?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.