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The correct answer is C.

OBJ-3.1: The \b delimiter indicates that we are looking for whole words for the complete string. The REGEX is made up of four identical repeating strings, (25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.”. For now, let us refer to these octets, such as the ones used in internet protocol version 4 addresses. Each octet will allow the combination of 25[0-5] OR (|) 2[0-4][9-] OR numbers 00-99 is preceded by (?) a 0 or 1, or just a single number followed by a “.”. Since the period is treated as a special character in a REGEX operator, the escape character (\) is required to enable the symbol to act as a dot or period in the output. This sequence repeats four times, allowing for all variations of normal IP addresses to be entered for values 0-255. Since 259 is outside the range of 255, this is rejected. More specifically, character strings starting with 25 must end with a number between 0 and 5 (25[0-5]). Therefore, 259 would be rejected. Now, on exam day, if you received a question like this, you can try to figure out the pattern as explained above, or you can take the logical shortcut. The logical shortcut is to look at the answer first and see that they all look like IP addresses. Remember, grep and REGEX are used by a cybersecurity analyst to search logs for indicators of compromise (like an IP address), so don’t be afraid to take a logical guess if you need to conserve time during your exam. So, which one isn’t a valid IP address? Clearly, 37.259.129.107 is not a valid IP address, so if you had to guess as to what wouldn’t be an output of this complex-looking command, you should guess that one!

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