Twentieth-century sculpture was more abstract than realistic, especially when artists depicted human form.
Option - C
Explanation:
With the word "was" which is the "singular past of be-verb" we can identify that the first part of the sentence is given in the past tense.
So, here in the blank, we have to use the past tense form of the word "depict" that is depicted.
Past Tense: It is used to describe situations or things that have happened already
(Example: yesterday, earlier in the day, ten years ago, last week).
