The global fertility rate (number of live births per woman) is given in the table as five-year averages from 1955 to 2015:

1955...........................................5
1960........................................4.9
1965........................................4.9
1970........................................4.8
1975........................................4.4
1980........................................3.8
1985........................................3.5
1990........................................3.3
1995...........................................3
2000........................................2.7
2005........................................2.6
2010........................................2.5
2015........................................2.4

a) Draw a time series graph of this data.

b) Comment on whether linear regression can be used on this entire data set to forecast the global fertility rate for 2020, either directly or by transforming the data using logarithms, squares, or square roots.

c) Transform the data using log(fertility rate - 2), and choose the part of the data set from 1970 onward. Use a linear regression (checking the conditions) to forecast the global fertility rate in 2020. Give a reason for subtracting 2 from the fertility rate and for choosing only the data from 1970 onward.