The underwriters' right to buy up to an additional 15% of shares in a public offering to meet overallotments of subscriptions for the offering is called:
Answer: (a), greenshoe option
In public offerings, underwriters are typically granted the right to buy 15% more shares of the offering to meet excess demand for the offering. This is referred to as an overallotment option or a Greenshoe option. The name came from the Green Shoe Company, which first used such an option.