The form of direct marketing with the lowest business expenditures is e-mail.
E-mail marketing typically involves minimal costs compared to other forms of direct marketing. There are no expenses associated with physical materials, postage, or printing.
Instead, the e-mail marketing relies on electronic communication, making it a cost-effective option for businesses.
Also, e-mail marketing allows for easy targeting and personalization which further enhance its cost-efficiency by reaching the right audience with tailored messages.
Therefore, the Option B is right.