He was very tired. He agreed to help me with my homework.

Translation: He was very tired at that time. He agreed to help me with my homework. (implying: even though very tired, still help with homework)

This is a question about grammatical structure, so don’t translate the answer but consider the structure.

To connect two clauses with the meaning of concession, the conjunction “although/ though/ even though/ even if’ – although – is often used according to the following structure:

Although/ though/ even though/ even if + S1 + V1+…, S2 + V2 + ….

If you do not use conjunctions, you can use two prepositions “in spite of” and “despite” – although – to connect sentences according to the following structure:

Despite/ in spite of + Noun/ V-ing, S + V +

In addition, there is a special structure for adjectives and adverbs as follows:

Adj/ adv + though/ as + S1 + V1 +…, S2 + V2 + …

All cases of concatenating concession clauses above will not be allowed to go with “but” or synonyms of “but”.

Considering 4 answers, we have:

Answer D is correct because it uses the special structure “Adj + as + S1 + V1. .., S2 + V2 +…” Answer A is incorrect because it uses the wrong structure.

Answers B and C are incorrect because there is “but”.