Why are reputation filters typically the first filters that are applied to inbound emails in content security systems?

Why are reputation filters typically the first filters that are applied to inbound emails in content security systems?
A. to remove spam messages, which use SMTP server resources.
B. These filters are the most complicated to run so they are executed first to conserve CPU resources.
C. to reduce the processing load on other filters by eliminating emails from known bad sources.
D. to reduce the processing load on other filters by eliminating emails from known bad sources.