The correct answer is: A. an equity share
An equity share is a type of security that represents ownership in a company. It is transferable merely by delivery, which means that the ownership of the share can be transferred from one person to another by simply handing over the share certificate.
A preference share is a type of security that gives the holder a preference over the holders of equity shares in the event of a company winding up. Preference shares are not transferable merely by delivery, but must be transferred in accordance with the terms of the preference share issue.
A share warrant is a document that entitles the holder to subscribe for a certain number of shares in a company. Share warrants are not transferable merely by delivery, but must be transferred in accordance with the terms of the share warrant issue.
A debenture is a loan that is secured against the assets of a company. Debentures are not transferable merely by delivery, but must be transferred in accordance with the terms of the debenture issue.
In conclusion, an equity share is the only type of security that is transferable merely by delivery.