Topic: Degree of Comparison,

Best Answer Explained in Below-:

The question "He is ... clever than his brother" requires an appropriate word to fill in the blank to form a grammatically correct comparison. In English, when making comparisons using adjectives, we often use comparative forms to indicate a difference in degree.

In this case, "clever" is an adjective meaning intelligent or smart. When comparing two entities for a certain quality, we can use the comparative form "more" for adjectives that do not take the "-er" ending, such as "clever." Therefore, the correct phrase would be "He is more clever than his brother," indicating that he has a greater level of cleverness in comparison to his brother.

Option A, "less," implies a reduced level of cleverness, which does not make sense in the context of the question. Option C, "very," is used to emphasize the degree of an adjective but does not work for comparisons. Option D, "much," could be used to enhance the comparison but doesn't stand alone correctly in this context. Thus, the most suitable and grammatically correct option is B) more.