Answer: a) An intermediary
Explanation: Intermediary is known as the link that is created between the two parties and link acts a mediator between them.It helps in bringing out the agreement or sharing of the facilities or other services .Intermediary acts as trading software between the buyer and the seller to keep the trading activity ongoing.
Other options are incorrect because marketplace is the marketing area where market products are found and purchased by the consumer, disintermediation is defined as having reduced number of mediator between two parties and sharing software is the sharing of software technology.Thus, the correct option is option (a).