Question: What are the average access counts of documents that have the functional area description "Acknowledgement"?
SQL: SELECT avg(t1.access_count) FROM documents AS t1 JOIN document_functional_areas AS t2 ON t1.document_code  =  t2.document_code JOIN functional_areas AS t3 ON t2.functional_area_code  =  t3.functional_area_code WHERE t3.functional_area_description  =  "Acknowledgement"