It looks like M is composed of all real numbers and that U = R also means its composed of all real numbers. This means that M and U are equal and both are composed of all real numbers.
To define the complement of M, it includes all values which are not in M. However, since M already has all real numbers and U doesn't have any values that M doesn't then the complement is nothing. It is an empty set with no items in it. This means A is the correct answer.
