What is the standard configuration of slave nodes in a Hadoop cluster?

A.
Each slave node either runs a TaskTracker or a DataNode daemon, but not both.

B.
Each slave node runs a JobTracker and a DataNode daemon.

C.
Each slave node runs a TaskTracker and a DataNode daemon.

D.
Each slave node runs a DataNode daemon, but only a fraction of the slave nodes run
TaskTrackers.

E.
Each slave node runs a TaskTracker, but only a fraction of the slave nodes run DataNode
daemons.

Explanation:
http://bradhedlund.com/2011/09/10/understanding-hadoop-clusters-and-the-network/
(second paragraph on the page)