The graph shows solar activity for the past 120 years. The y-axis points upward and shows the percentage of the Sun's surface covered by sunspots measured from 0.0 to 0.5 percent. The x-axis shows time from the year 1900 to about 2017. The plot is a frequently oscillating curve. The annual average is oscillating too, with a period of about 11 years, almost zero values at the ends of the periods, and high peaks in the middles of the periods. The height of the peaks varies from about 0.1 to 0.4 percent. The highest peak for the past 120 years is 0.5 percent around 1958. Study this figure and its axis labels. What is this graph showing us