The correct answer is B.
OBJ-1.5: The most complex password of these four options is 4@kn?Q9$. All four passwords are eight characters, so the most complex password will use the largest character set. As shown in the password 4@kn?Q9$, there are four character types: uppercase letters, lowercase letters, numbers, and symbols. The other options only use one, two, or three of these character types. This password uses all four, making it the most complex and secure option.