SAT Question c91ef0f0: Form Structure And Sense answer and explanation

English - Form Structure And Sense - Subject Verb Agreement
0:00
FREE OFFICIAL BANK
During the American Civil War, Thomas Morris Chester braved the front lines as a war correspondent for the Philadelphia Press. Amplifying the voices and experiences of Black soldiers ______ of particular importance to Chester, who later became an activist and lawyer during the postwar Reconstruction period.
158
Difficulty:Hard
Which choice completes the text so that it conforms to the conventions of Standard English?