which benefit is of using the dollar variable (as in $TARGET01)?

While creating queries in Cisco Security MARS, which benefit is of using the dollar variable (as in $TARGET01)?

A.
The dollar variable allows matching of any unknown reporting device.

B.
The dollar variable ensures that the probes and attacks that are reported are happening to the same host.

C.
The dollar variable enables the same query to be applied to different reports.

D.
The dollar variable enables the same query to be applied to different cases.