A contract is a legal transaction concluded by a mutual exchange of assents of two or more persons. Therefore, for the formation of a contract there is a need for two mutually declared intentions - offer and acceptance. An offer is a declaration of intention by one party, known as the offeror, whereby he expresses his willingness to enter into a contract. An offer, until it is terminated, gives the offeree a continuing power to create a contract by declaring an acceptance. An acceptance is a declaration of intention to agree to the terms of the offer. If all its elements are complete, a contract takes effect at the moment it is concluded. 

The offeror does not have to set a time limit. If no time limit is set, then the Code of Obligations makes a distinction between the parties who are present and who are absent. Where an offer is made in the offeree’s presence and no time limit for acceptance is set, it is no longer binding on the offeror unless the offeree accepts it immediately. Offers declared by telephone, computer or other communication tools, on the condition that the parties understand and respond simultaneously, are considered to be made in the offeree’s presence. Thus, physical presence is not required for a contractual offer.

The correct answer is C.