For each of the following examples state whether the data are numerical or categorical, and state whether the data are cross-section, time series, panel or observational data. {a} Data on annual health expenditures in 2018 for the US. by use of funds. (b) Data on whether the Dow Jones Index at the close of trading was at a higher or lower value than at the close of trading the preceding trading day. {c} Data on sales this quarter by each of 23 sales representatives. (d) Data on the price of 1 gigabyte of computer disk storage each year from 1980 to 2018. {e} Annual earnings of 153 individuals in each of the years 2010 to 2018