Final answer:
John should select Data labels to identify the exact value for each column in his chart, as they display the precise data value on the chart itself.
Step-by-step explanation:
To identify the exact value that each column in his chart represents, John should choose a) Data labels. Data labels are used to display the actual data or value associated with each point or column in a chart, which makes it easy to read the precise value without having to estimate from the axis. The other options, such as Axis title, Legend, and Trendline, serve different purposes. The Axis title gives information about what the axis represents, including the variable name and units of measurement (e.g., Time (min) for the x-axis), while a Legend explains the symbols or colors used in the chart to represent different datasets or categories. Lastly, a Trendline is drawn to illustrate the overall trend or relationship between the variables in the data, and does not give the exact values of individual data points.