Which graph would you require to get a visual expression of time series data? Explain which trend model should be used in case the time series data rejects the following types of graphs:

a. straight line trend.

b. long term downward or upward quadratic movement.

c. increase at a rate such that the percentage difference from value to value is constant.

d. Among the models you get as an answer in (a), (b) and (c), how would you determine which model to choose?