4. The following results come from a dataset that contains information on a random sample of 534 U.S. workers surveyed in 1985. The dataset contains information about the hourly wage (in U.S. dollars) and the sex of each of the workers surveyed, as well as information about each worker's age (categorized into 4 quartiles), union membership, job type (collapsed into 8 different categories), marital status (married or not), and occupational sector (3 categories). You are interested in assessing the relationship between hourly wages and sex in the population of workers from which the sample was taken. Forty-six percent of the sample is female, and the overall average hourly salary for the 534 workers is $9.00 per hour (in 1985 dollars). You are reviewing the following set of salary mean difference estimates comparing female and male workers. The first estimate is the unadjusted association, and the subsequent estimates in the table have been adjusted for the characteristics listed. Table 1: Unadjusted and Adjusted Mean Salary Differences for Sex Index Estimate Estimate is Adjusted for: A $2.12 50.44 (unadjusted) $2.14 $0.43 Age $1.99 $0.43 Age, Union Membership mon -$1.92 $0.43 Age. Union Membership, Job Type $2.01 $0.43 Age, Union Membership, Job Type, Sector, Marital Status Standard Error of the Mean Difference - What two groups mean does the mean wage difference, adjusted for age and union membership (C) compare? a. Females to males. b. Females to males of the same age. c. Females to males of the same age and union membership status. d. Females to males of the same age, union membership status and job type. e. Females to males of the same age, union membership status, job type, occupational sector, and marital status