Answer:
(a) Bar chart
Explanation:
A bar graph or a bar chart is a graphical representation of data and it belongs to the frequency graphs. It is the best way to illustrate the frequencies of political preference because it is very easy to interpret and it shows the relative sizes that are we can see which political preference is the most common and which is the least, at one glance.
Therefore, we can say that
The best way to illustrate the frequencies for each political preference is a bar graph.
Hence, the option (a) is correct.