Executive functioning is best defined as:

Executive functioning encompasses a range of cognitive processes that enable individuals to plan, focus attention, remember instructions, and juggle multiple tasks successfully. Specifically, it involves the mental skills that are necessary for goal-directed behavior, such as problem-solving, organizing, and regulating emotional responses.

When we refer to executive functioning, we're discussing how the brain manages complex tasks and priorities, which is critical not only in academic settings but also in daily life. This includes the ability to set and achieve goals, adapt to changing situations, and self-monitor one's actions. This definition highlights the essential nature of these cognitive processes in facilitating effective functioning across various contexts, making option B the most accurate choice.

The other options do not encompass the full breadth of what executive functioning entails. For instance, physical exercises for brain health would not capture the cognitive complexity needed for goal-directed behavior, while equating executive functioning to a memory deficit or a method of teaching would limit its scope and application significantly. Thus, option B stands out as the most comprehensive definition.