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Since the sentence uses past tense, so answer (a) and (c) must wrong.
This leaves only (b) and (d).
You may think, since the case of "his return" has not realised yet, so we should use "would come". It is true but partially. The answer should be (b) came.
There is tense simplification in subordinate clauses. Subordinat clauses refer to the clauses which is not the main/parent part of the statement.
So if the main verb of a sentence make sit clear what knid of time the speaker is talking about, it is not necessary for the same time to be indicated again in the subordinate clauses. It is also used to make the sentence neater and less clumsy.