A tombstone ad: a. is permitted in Regulation D offerings.
b. is an offer to sell securities.
c. can be run prior to the effective date of the registration.
d. all of the above

Option c: Can be run prior to the effective date of the registration

Explanation:

Tombstone Advertisements is simply a form of advertisement that provides a listing of the underwriting group or organization that are found to be actively involved in the new offering in addition to basic information on the offering. It is usually used during and after the waiting period.

chronological thinking is an indispensable tool to structure a historical narrative and to give meaning to a sequence of events. the final section presents the results of a survey to test the chronological thinking of lower secondary school students carried out by the educational research institute.