"Are they in the UK?"
I typed "他们在英国吗?" and was told I had the wrong answer. IIRC, 他们 and 她们 both mean "they", so I'm not sure why this was marked wrong.
They do both mean 'they' but it's the difference between a female-they and a male or female and male they. There is no tonal difference but only a written difference which sucks if you have to translate it like that