Appear at an exhibition (4)
I believe the answer is:
show
I believe this is a double definition.
'appear' is the first definition.
(I know that show is a more specific form of the action appear)
'an exhibition' is the second definition.
(I know that show is a type of exhibition)
'at' is the link.
(Other definitions for show that I've seen before include "Performance" , "Display; prove" , "Labour's evidence for starting" , "Demonstrate; spectacle" , "Musical featuring 'Old Man River'" .)