Among the various kinds of visual aids, tables are a. the most difficult to construct b. the most common aid used in reports c. for showing the relationships between two sets of data d. generally used to show trends in business performance

a.the most difficult to construct 
Textual features act as signposts, or clues, to help readers of business documents. Originally, textual features are classified as the directional text features, supplementary text features, and visual aids. The directional text features are used to help the readers locate specifics on the text, may it be page numbers or chapter headings. Supplementary text features refers to indexes, footnotes and bibliographies that may seem important for the readers. Visual aids are those that help the readers visually understand the text on the book. In business documents, these textual features refers to clues or signposts to hasten or help the reader in navigating through the documents.