Opinion vs thought vs idea vs attitude

Please look at the exercise below:
1.After listening to all the arguments I am now of the … that there should be no new road.
A.attitude B.opinion C.thought D.idea
The correct answer is B,but what about the others ? :frowning:
Please help me.
Thanks in advance

This is a set phrase: “to be of the opinion of”[YSaerTTEW443543]

TOEFL listening lectures: A university lecture by a professor of Paleontology[YSaerTTEW443543]

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I’d say the set phrase is “be of the opinion (that)”.
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You’re right, Amy.[YSaerTTEW443543]

TOEFL listening lectures: A university lecture by a professor of Natural History[YSaerTTEW443543]