If You Saw a Graph with Rectangles Standing on a Horizontal

If you saw a graph with rectangles standing on a horizontal axis, what is the best immediate visual clue to determine whether it is likely to be a well-designed bar chart or a histogram?

A) If it is in color or shades of gray.
B) If the bars are solid or filled with patterns.
C) Whether the bars touch or have gaps between them.
D) Whether the y-axis goes to zero or some other number.