SecureXL is a technology that accelerates the performance of the Check Point Security Gateway by offloading CPU-intensive operations from the Firewall kernel to the SecureXL device. SecureXL can handle various types of traffic, such as TCP, UDP, ICMP, non-IP, VPN, NAT, etc. SecureXL can also work with various features, such as CoreXL, ClusterXL, QoS, etc.

One way to indicate that SecureXL is enabled is to use the fwaccel commands in clish. Clish is a command-line shell that provides a user-friendly interface for configuring and managing Check Point products. The fwaccel commands are used to control and monitor SecureXL operations, such as enabling or disabling SecureXL, viewing SecureXL statistics, managing SecureXL templates, etc. For example, the command fwaccel stat shows the status of SecureXL, such as whether it is on or off, how many packets are accelerated or not accelerated, etc.

The other options are not valid indicators of SecureXL being enabled:

A. Dynamic objects are available in the Object Explorer: Dynamic objects are objects that represent IP addresses that change over time, such as VPN clients, DHCP clients, etc. Dynamic objects are available in the Object Explorer regardless of whether SecureXL is enabled or not.

B. SecureXL can be disabled in cpconfig: Cpconfig is a command-line tool that allows you to configure various settings of Check Point products, such as administrator password, GUI clients, SNMP extension, etc. SecureXL can be disabled in cpconfig only if it was enabled before. Therefore, this option does not indicate that SecureXL is enabled.

D. Only one packet in a stream is seen in a fw monitor packet capture: Fw monitor is a command-line tool that allows you to capture and analyze network traffic passing through the Security Gateway. Fw monitor shows the traffic at different inspection points in the Firewall kernel. If SecureXL is enabled, some packets may be accelerated by SecureXL and bypass the Firewall kernel inspection. Therefore, fw monitor may not see all packets in a stream. However, this does not mean that only one packet in a stream will be seen by fw monitor. Some packets may still go through the Firewall kernel inspection and be seen by fw monitor. Therefore, this option does not indicate that SecureXL is enabled.

Therefore, the correct answer is C.

References: How to enable/disable Check Point SecureXL via CLI, Part 3 - SecureXL, What is SecureXL?, Clish - Command Line Interface Shell, sk30583: What is FW Monitor?