In the sentence "James is <em>more</em> smarter than Steven" the problem is the use of the comparative word more because the word smarter is already forming the comparative: adjective smart + er. This is the proper way to show the comparative of <em>short</em> adjectives. For <em>long</em> adjectives (expensive, beautiful, etc) the comparison is made with more + adjective + than (more expensive, more beautiful).
The problem in the sentence "James is more smarter than Steven", is option A. Double Comparison. Double comparison happens when we use the word more or less plus the comparative form of an adjective with the suffix -er.
