Can I say? 1 If I and the hearer don't know the sex, can I say both: a. If you meet someone today, that person / this person had better be a doctor. b. If you meet someone today, they had better be a doctor. 2 If I and the hearer don't know the sex, can I say both: a. There was someone who snuck into my house last night. - That person was a thief, weren't they? b. There was someone who snuck into my house last night. - They were a thief, weren't they? Thanks!