CompTIA Linux+ XK0-005 (v7) Practice Question

A Linux administrator is writing a Bash script to verify whether a target host is reachable before launching an application. During testing, she places diagnostic echo statements inside the control structure. Examine the excerpt:

ping -c1 "$HOST" >/dev/null 2>&1
_____ [ $? -eq 0 ]; then
    echo "Host reachable - starting service"
    systemctl start app.service
else
    echo "Host unreachable - aborting"
fi

Which shell keyword should replace the blank so the script executes the appropriate branch based on the success or failure of the preceding command?