Final answer:
Gerrymandering (option a) is a technique that has been used to dilute the political influence of minorities, but it can also be utilized to enhance minority representation by creating majority-minority districts.
Step-by-step explanation:
One of the techniques that were used to prevent minorities from electing their own representative, but can also be used to promote minority's power to elect their own representative, is gerrymandering. Although typically used to dilute the political influence of minority groups by spreading them thinly across multiple districts (cracking) or concentrating them in one (packing), gerrymandering can also be employed to create majority-minority districts.
This approach intentionally draws the boundaries to create a district where a minority population constitutes the majority to enhance their electoral power and representation in Congress. Despite the questionable ethics behind gerrymandering, it has been legally used to increase the number of African American representatives and can similarly be utilized to empower other minority communities when drawing legislative districts.