The Framingham Heart Study began in 1948 with 5,209 adult subjects, who have returned every two years for physical examinations and laboratory tests. The study now includes the children and grandchildren of the original participants. Identify the following data as cross-section, time series, or panel data:

a. The number of people who died each year from heart disease.

b. The number of men who smoked cigarettes in 1948, 1958, 1968, and 1978.

c. The ages of the women in 1948.

d. Changes in HDL cholesterol levels between 1948 and 1958 for each of the females.