Choose the correct alternative which will improve the part of the sentence given in quotes.
The black sky 'was illuminated' by forked lightning.

Correct option is D

No improvement is needed as "was illuminated" is correctly used.
Explanation: The phrase "was illuminated" correctly uses the passive voice to indicate that the action (illuminating) was performed on the subject (the sky) by an unspecified agent (lightning). This structure is appropriate for the context where the focus is on the action happening to the subject.
Grammatical rule used: Passive voice is used when the focus is on the action or the recipient of the action rather than the doer.
Example: The room was illuminated by bright lights.