In this android application, in pronoun test, they have a question
If anyone calls,tell ___________ that I'll be back in half an hour
option 1 : his/her option 2 : him/her option 3 : them option 4 : None of these
At first instance, the sentence that I can read fast is
If anyone call tell them that I'll be back in half an hour.
But as everyone refers singular, I thought it'd be
so the answer should be
If anyone call tell him that I'll be back in half an hour.
But the application shows right answer as
option 1: his/her
Even reading as
If anyone call tell his that I'll be back in half an hour.
doesn't sound pretty well.
So what answer is right, anyone just clarifies me that how to use his/him depending on the context and semantics of the sentence.