What is a difference between maxconcurrency and plannedconcurrency?

A.
Maxconcurrency is a hard limit to the number of queries running within a pool;
plannedconcurrency is used to create a query budget.

B.
Maxconcurrency is used to create a query budget; plannedconcurrency is a hard limit to the
number of queries running within a pool.

C.
Maxconcurrency is a hard limit to the number of queries running within a pool;
plannedconcurrency limits the number of queries running on the cluster.

D.
Maxconcurrency limits the number of queries running on the cluster; plannedconcurrency is a
hard limit to the number of queries running within a pool.

Explanation: