Answer:
The objective complement in the sentence is: frightened.
Step-by-step explanation:
An objective complement can be defined as a noun, an adjective, or a pronoun that complements the meaning of the verb and, at the same time, modifies the verb's direct object.
Let's apply the definition above to the sentence "The last scene left the audience frightened." The verb is "left" and its meaning is completed by "audience frightened." To find the direct object, we can ask the verb a question. The scene left what or who? The audience. But notice that this is not enough. Something is missing. The audience was left what? Frightened. Thus, the adjective "frightened" is modifying "audience" and completing the meaning the meaning of the verb.