As a condition of registration a prospectus approved by the securities commissioner shall be sent or given to each person to whom an offer is made before or concurrently with (a) the first written offer made to him, otherwise than by means of a public advertisement, by or for the account of the issuer or any other person on whose behalf the offering is being made or by any underwriter or broker-dealer who is offering part of an unsold allotment or subscription taken by him as a participant in the distribution, (b) the confirmation of any sale made by or for the account of any such person, (c) payment pursuant to any such sale or (d) delivery of the security pursuant to any such sale, whichever first occurs.