What apt-get command would you run to download the latest list of packages, but not the packages themselves?

This answer is wrong. Correct answer is A. apt-get update

apt-get(8) – Linux man page

Name
apt-get – APT package handling utility – command-line interface

Synopsis
apt-get [options] [-o config=string] [-c=cfgfile] command [pkg]

Description
apt-get is the command-line tool for handling packages, and may be considered the user’s “back-end” to other tools using the APT library. Several “front-end” interfaces exist, such as synaptic and aptitude.

Commands
Unless the -h, or –help option is given, one of the commands below must be present.

update
Used to re-synchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list(5). An update should always be performed before an upgrade or dist-upgrade.

upgrade
Used to install the newest versions of all packages currently installed on the system from the sources enumerated in /etc/apt/sources.list(5). Packages currently installed with new versions available are retrieved and upgraded; under no circumstances are currently installed packages removed, nor are packages that are not already installed retrieved and installed. New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version. An update must be performed first so that apt-get knows that new versions of packages are available.