Select the most appropriate option that can substitute the highlighted segment in the given sentence.
I regarded my brother on passing his graduation examination.

Correct option is A

Option (a) "congratulated" is the most suitable choice.
The highlighted segment "regarded my brother on passing his graduation examination" seems to suggest that the speaker had a positive and respectful feeling towards their brother for achieving this milestone.
Therefore, the most appropriate option to substitute this segment would be: (a) congratulated - This means expressing approval and pleasure for someone's achievement, which fits the context.
Meanings for the other options:
 Disparaged - This means to criticize or belittle, which is the opposite of what the sentence conveys.
 Flattered - This means to praise or compliment someone excessively, but it doesn't quite fit the context of the sentence.
 Kowtowed - This means to show excessive respect or submission, often beyond what is necessary, which is not exactly what the sentence implies.