This exercise gives "Jesteście członkami tej fundacji?" as a translation of "Are you a member of this foundation?" but "a member" shows the question is addressed to one person, not a group.
Good point, reported it. Thanks for noticing.
"Czy pan(i) jest członkiem tej fundacji"?
In a question like this which is virtually the same as a statement it would be worth including a question mark
"Czy jesteś człowiekiem tej fundacji?" ?
Are you a person of this foundation? Weird...
Sorry, I meant członkiem, but my question was about using czy, so I didn't notice the rest of my sentence had a mistake.