When documenting a direct quotation for a source with one author, which is correct?

Question $6$ Select one:

a$.$

Sanders explains that economic woes are due to $$the mortgage crisis and poor risk assessment $(20).$

b$.$

Sanders explains that economic woes are due to $$the mortgage crisis and poor risk assessment$(20).$

c$.$

Sanders explains that economic woes are due to$,$the mortgage crisis and poor risk assessment$(20).$

d$.$

Sanders explains that economic woes are due to $$the mortgage crisis and poor risk assessment $(20).$