If this sentence is changed to passive voice, then the subject is also changed, in order to retain the meaning of the sentence.

So, the object takes the place of the subject and vice versa and the word 'by' is introduced as now the subject receives the action by the object. The verb form of the sentence is also changed from active form to passive.

'Subject (I) + verb (expected) + object (him) + infinitive phrase (to give us financial aid)' changes to:

'New subject (It) + verb (was expected) + by + new object (me) + relative clause (that he will give us financial aid)'

This can be seen in option C, hence it's the right answer.

Also, the action 'expected' is not being received by the object 'him', since the verb 'expect' is an assumption. Also, if we change the object 'him' to the subject: 'He was expected by me to give us financial aid.' sounds a bit strange. Hence we begin the sentence with 'it' and add a relative clause 'that he will give us financial aid'.

Option A: The words 'by me' are missing. Because of that, the sentence has slightly changed in meaning.

Option B: This sentence too has changed in meaning. The phrase 'let it be expected' is imperative, whereas the original sentence is assertive.

Option D: The modal verb 'may' expresses a possibility. But the word 'may' is not a part of the original sentence. Also, 'he may expect' is in active voice.