Can I say "utmost" instead of "foremost" here? Or do they have different nuance?
No, you can't replace "utmost" with "foremost" here. Although these words have similar meanings, they aren't used interchangeably; I am unsure why. "Utmost" means most significant or most extreme. It's used to emphasize how important something is. "Foremost" means very important or urgent. Ex: She shall be treated with the utmost care. Ex: This business deal needs to be treated with the utmost importance. Ex: Dr. William Abdu is one of the foremost doctors in the world. Ex: He is the foremost lawyer in the county.
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