"I was standing behind him."
Translation:Я стоял за ним.
Why isn't this word order accepatable? "за ним я стоял" ----- the correct answer in a previous sentence in the exercise was "За ними стоит женщина". A woman is standing behind them". the same word order
This is a rather unnatural order. I can imagine you uttering this in a heated manner, when someone accuses you of queue jumping (with stress being put on "за ним"), but hardly otherwise.
See zirkul's reply to servolock just above.
I'm no expert but I have to say, while some Russian word order sounds unusual to my US English ear, the Russian sentence you (and servo) said sounds positively Yoda-tastic.
“Looking? Found someone you have, eh?”