This paper defines visual explanations to the Verification Problem in argumentation, that is, of why a set of arguments is or is not acceptable under a given semantics. These explanations rely upon the modularity of the acceptability semantics, and they take the form of subgraphs of the original argumentation graph. Graph properties that these subgraphs satisfy depending on whether or not the set is acceptable, are established. Properties of the proposed explanations are addressed, and the potential of the modularity of the approach is highlighted. Note that this research report is the complete version of a paper submitted to a conference. In this complete version, the reader can find the proofs of the results given in the submitted paper.