Opinion vs thought vs idea vs attitude

[Duc]

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 ? :(
Please help me.
Thanks in advance
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Don't see your shade think you are great

[Torsten]

This is a set phrase: "to be of the opinion of"

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

[Yankee]

.
I'd say the set phrase is "be of the opinion (that)".
.
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"Nearly all men can stand adversity, but if you want to test a man's character, give him power." ~ Abraham Lincoln

[Torsten]

You're right, Amy.

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