Descriptions are provided for several types of series: random, stationary, with a trend, or seasonal. Identify each type of series.

a. A series having basic statistical properties, such as the mean and variance, that remain constant over time.

b. The successive values of a time series are not related to each other.

c. A high relationship exists between each successive value of a series.

d. A significant autocorrelation coefficient appears at time lag 4 for quarterly data.

e. A series that contains no growth or decline.

f. The autocorrelation coefficients are typically significantly different from zero for the first several time lags and then gradually decrease toward zero as the number of lags increases.