Frieda and Joseph currently receive an OAS pension, and they are curious to know if they are eligible to receive the Guaranteed Income Supplement. To determine their eligibility for the supplement, they should know that for each pensioner the maximum supplement will be reduced by: O a) $1 for every $1 of their combined income (not including OAS benefits) in the previous year Ob) $1 for every $4 of their combined income (not including OAS benefits) in the previous year c) $1 for every $2 of their combined income (including OAS benefits) in the previous year O d) $3 for every $4 of their combined income in the previous year