Which of the following resources can be directly limited for a given user using ulimit? (Choose three correct answers.)

`ulimit -t` sets the maximum amount of CPU time in seconds that a process can use, making 'Maximum seconds of CPU time spent' a directly limitable resource.

`ulimit -n` sets the maximum number of open file descriptors, also known as open files, that a user's processes can have.

`ulimit -u` sets the maximum number of user processes (or threads) available to a single user, preventing one user from spawning too many processes.

`ulimit` does not directly control the 'Maximum number of concurrent login sessions'; this is typically managed through PAM or other system-level configuration, not directly by `ulimit`.

`ulimit` does not limit the 'Maximum seconds of login duration per session'; this type of limit is usually managed by other system-wide or service-specific configurations.