Help pls I don’t underestand and I just want to finish this

Has the marrying age of a man changed over the years? the united states bureau of the census takes formal count of everyone in the u.s. every 10 years and has provided the following data that gives the median age of an american man at time of his first marriage. year median age 1910 25.1 1920 24.6 1930 24.3 1940 24.3 1950 22.8 1960 22.8 1970 23.2 1980 24.7 1990 26.1 2000 26.8 what does a rate of change of zero mean in this situation? a. the median age of a man at the time of his first marriage is, on the average, constant. b. the median age of a man at the time of his first marriage is, on the average, decreasing. c. the median age of a man at the time of his first marriage is, on the average, increasing. d. the rate of change cannot be zero in this situation.