Choice "B" is correct. E-cash (also called digital cash) is currency in an electronic form that moves outside the normal channels of money. It maintains financial privacy just like real cash does. PayPal is a form of digital cash.
Choice "c" is incorrect. A credit card cannot be used to pay for goods or services while maintaining (complete) financial privacy. While a particular site may be very secure, the mere fact of presenting the credit card does not maintain financial privacy.
Choice "d" is incorrect. A "site draft" (which is actually a "sight draft" which means that it can be seen) is a draft, a negotiable instrument that is payable on demand. It does not maintain (complete) financial privacy any more than a check does.
Choice "a" is incorrect. An electronic check does not maintain financial privacy any more than a paper check does.