How to us futile in an sentence?

He sighed at the futile thoughts. Several futile attempts have been made to draw conclusions as to the intelligence of various birds. His negotiations with Russia proved futile, and after a year's absence he returned to New York.

The definition of futile is something that won't succeed or is unimportant. An example of futile is someone trying to stop a plane that has already left the ground. Having no useful result; ineffectual. ... Incapable of producing results; useless; not successful; not worth attempting.

Explanation:

She sighed at the futile thoughts

Explanation:

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i believe the answer is a

the noble might have thought that the system was far because they had lot of things and riches and the serf would have thought that the feudal system was un fair because of the way they were treated.