One drawback of Application Level Firewall is that it reduces network performance due to the fact that it must
analyze every packet and:

A.
decide what to do with each application.

B.
decide what to do with each user.

C.
decide what to do with each port.

D.
decide what to do with each packet.

Explanation:
The application firewall is typically built to control all network traffic on any OSI layer up to the application layer.
At the lowest level the application firewall can examine each data packet. This slows down the performance.
Incorrect Answers:
A: Making decisions at the application level would not slow down the firewall.
B: An application firewall cannot make decisions based on the user.
C: Making decisions at the port level would not slow down the firewall, especially compared deciding what to do
with each packet.

https://en.wikipedia.org/wiki/Application_firewall