10.18 Civil disorders. The years around 1970 brought unrest to many U.S. cities. Here are government data on the number of civil disturbances in each three-month period during the years 1968 to 1972. (a) Make a line graph of these data. (b) The data show both a longer-term years. Describe the nature of both trend and seasonal variation within patterns. Can you suggest an expla- nation for the seasonal variation in civil disorders? Period 1968, Jan.-Mar. Count 6 Apr.-June 46 Period 1970, July-Sept. Oct.-Dec. Count 20 6. July-Sept. 25 1971, Jan.-Mar. 12 Oct.-Dec. 3 Apr.-June 21 1969, Jan.-Mar. 5 July-Sept. 5 Apr-June 27 Oct.-Dec. 1 July-Sept. 19 1972, Jan.-Mar. 3 Oct.-Dec. 6 1970, Jan.-Mar. 26 Apr.-June July-Sept. 8 5 Apr-June 24 Oct.-Dec. 5 u in