Translation:They admire her.
The lu- prefix indicates that there is a third person singular object, i.e. "him", "her", or "it". The Klingon sentence does not actually make it clear which is meant. Klingons are fine with that ambiguity, but in English you have to pick one. Which one is intended will usually be clear from context, but since Duolingo does not provide context, you just have to randomly pick one. When showing you the "best" answer Duolingo also randomly picks one, so sometimes it might say "him" or "it". When you are entering your translation it will accept any of the three options as correct.