which there is no proxy?

In which of the following firewalls are the incoming or outgoing packets blocked from
accessing services for which there is no proxy?

A.
Circuit level firewalls

B.
Packet filters firewalls

C.
Stateful multilayer inspection firewalls

D.
Application level firewalls

Explanation:

Reference:
http://www.vicomsoft.com/learning-center/firewalls/