An engineer has created a bash script to automate a complicated process. During script execution, this error occurs: permission denied. Which command must be added to execute this script?

chmod +x modifies the file's permission bits to add the execute flag for the owner, group, and others, which directly resolves a 'permission denied' error when attempting to run a shell script. Without this flag set, the operating system refuses to execute the file as a program regardless of its content.

source reads and executes the script in the current shell context without requiring the execute bit, but it does not grant execute permission and is not the standard fix for a permission denied error.

chroot changes the apparent root directory for a running process and has no relationship to file execute permissions.

sh ex.sh invokes the shell interpreter directly with the script as an argument and bypasses the execute permission check, but it does not add execute permission to the file itself as the question requires.