The scenario requires controlling how AS 111 sends its outbound traffic (egress traffic). BGP policy control for outbound traffic is best handled via manipulating the BGP Local Preference attribute, as:

Local Preference (LocalPref) influences path selection for outbound traffic by setting a preference for one path over another.

It is evaluated within the AS and does not require coordination with external autonomous systems.

LocalPref changes are fully contained inside AS 111 and satisfy the requirement to only affect AS 111.

A higher Local Preference value is preferred, thus you set higher values for routes learned via AS 100.

Why other options are incorrect:

A (community): Typically influences inbound traffic or interacts with upstream providers.

B (MED): Influences inbound traffic for external neighbors, not outbound.

D (AS Path): Also primarily influences inbound traffic selection by remote ASes.