What to answer if immigration authority asks about "why H1B w/o COS"?

What to answer if immigration authority asks about “why H1B w/o COS”?

I was on H4 and filed for H1B this year. I have to go to India for an important event and everyone advised me against going. Not on H1B status at least. So I'm going on H4 and will do the change of status after I come back in Dec



What should I tell immigration officers when they ask me "why H1B without change of status?"



TIA,



SP