Answer: B) Similarity
Step-by-step explanation:
Similarity in terms of Gestalt principles is defined as combination of elements takes place in the form of grouping if similarity between traits, shape, color , texture etc of elements are present.Similar elements can be perceived easily than dissimilar elements.
According to the question, Carol is displaying similarity because she is able to perceive or recognize letters of school accordingly as band members spell it.
Other options are incorrect because closure, symmetry or proximity are not the principle for describing integration of element id they have similar traits.Thus, the correct option is option(B)