A 68 year old taxpayer received Social Security benefits of $18,000, wages of $4,000, interest and dividends of $5,000, unemployment compensation of $3,000 and municipal bond interest of $2,000. Given the single taxpayer base amount of $25,000 for calculating the social security income exclusion, what is the taxpayer's adjusted gross income?

A) $23,000

B) $9,000

C) $12,000

D) $21,000