The correct option is A Most
Option C: 'Most' is an adjective that describes the noun in terms of number. It means 'greatest in amount or degree'. Here, it refers to the greatest number of people. It is the only option that modifies the noun 'people', hence C is correct.
Option A: 'The most' expresses a comparison in a sentence. It is placed in front of an adjective, and not a noun. For example, 'The most interesting thing happened today.' Hence, this option isn't correct.
Option B: 'Most of' is usually followed by 'the', and is placed before a specific set of something. In contrast, the given sentence does not refer to a specific set of people. In this case, 'most' is used on its own as it refers to the 'majority of something in general'.
Hence option B is incorrect.
Option D: 'A great' is grammatically incorrect because it holds no meaning, unless it's followed by words like 'number of' or 'deal of'; 'a great number of people', 'a great deal of money'.
Hence option D is incorrect.