I didn't know -----they would have a meeting here the next week应填什么

I didn't know -----they would have a meeting here the next week应填什么
I didn't know -----they would have a meeting here the next week
应填什么

I didn't know -----they would have a meeting here the next week应填什么
whether 或是 if

if/whether是否

我觉得只能填whether