Answer A: the moon is the most brilliant object in the sky.
Sentence A uses correctly <em>the most</em> before the adjective <em>brilliant</em> to make this degree of comparison, the <em>superlative</em>. Brilliant has three sylllables, but if it was a <em>short</em> adjective, the superlative would need <em>the</em> +<em>est </em>instead of most. Examples: tall - the tallest; dark - the darkest etc. In B, there is no comparison. In C the correct use for <em>more </em>is to compare two things/persons. <em>Mary is </em><em>more</em><em> beautiful </em><em>than</em><em> her sister.</em>
