the complete sentence would be: "My younger brother looked ill last night, and was evidently worse this morning."

This construction properly indicates a decline in his health from the previous night to the morning.

Option A, "worse," is the comparative form of "ill," which fits the context of the sentence.

Option B, "worst," is the superlative form and does not fit the comparative comparison needed in this sentence.

Option C, "more ill," is also a valid choice but is less concise than the simpler and more common term "worse."

Options D and E are unrelated to the context of the sentence.