The answer is the fourth option:
4. Cassius cannot believe that a weakling like Caesar has become so great.
From the excerpt we can understand that Cassius is incapable of believing that the man he once saw pale and sick is the same man that rules others. He compares Caesar to a sick girl and criticizes his weakness. As he states, 'it doth amaze me (that) a man of such a feeble temper should so get the start of the majestic world, and bear the palm alone.'
In act 1, scene 2 of Julius Caesar, Cassius is trying to convince Brutus that Caesar is not better than any of them, that they should not be his subjects. He tells Brutus that people talk of him (Brutus) as a noble man whom they would very much like to follow instead of Caesar.