what is the most likely cause for this slowdown at the database level?

A database exists as a read-intensive server that is operating with query_cachek_type =
DEMAND. The database is refreshed periodically, but the resultset size of the queries does
not fluctuate. Note the following details about this environment: A web application uses a
limited set of queries. The Query Cache hit rate is high. All resultsets fit into the Query
Cache. All queries are configured to use the Query Cache successfully. The response times
for queries have recently started to increase. The cause for this has correctly been identified
as the increase in the number of concurrent users accessing the web service. Based solely
on the information provided, what is the most likely cause for this slowdown at the database
level?

A.
The Query Cache is pruning queries due to an increased number of requests.

B.
Query_cache_min_res_unit has been exceeded, leading to an increased performance
overhead due to additional memory block lookups.

C.
Mutex contention on the Query Cache is forcing the queries to take longer due to its
singlethreaded nature.

D.
The average resultset of a query is increasing due to an increase in the number of users
requiring SQL statement execution.