He, she or they
If you’re not sure whether you’re talking about a man or a woman, use ‘they’ or ‘their’ as the pronoun.
We got a missed call from someone this morning, but they didn’t leave a message.
One of the people at this morning’s workshop left their notebook on the table upstairs.
There’s no singular pronoun in English that covers both sexes. So traditionally people have gone for ‘he’ or ‘his’ when they didn’t know if they were referring to a Larry or a Lucy – because we’ve always been a bit sexist like that. But singular ‘they’ has actually been around for a very long time: you can find it in Chaucer, Shakespeare and even the US Declaration of Independence. And it’s the 21st century now, so there’s no excuse for that kind of nonsense.