Answer:
The command that can be used to install the latest versions of all packages currently installed on the system from the sources configured in sources.list is "sudo apt-get update && sudo apt-get upgrade". This command performs two actions: first, it updates the package index files from the sources listed in sources.list, and then it upgrades all installed packages to their latest versions available from the updated sources. However, it does not remove any packages that are no longer needed. To remove such packages, one can use "sudo apt-get autoremove".