Which product has been a popular limited-time offering during summer seasons?

The Shamrock Shake is a product that McDonald's has famously offered as a limited-time item, particularly during the St. Patrick's Day season, which often falls in the early spring but has also been associated with the summer promotional timeline in some regions. Its unique mint flavor has become iconic and eagerly anticipated by fans, contributing to its popularity during promotional periods.

While the McFlurry and Strawberry Sundae are popular items on the McDonald’s menu, they are not strictly limited-time offerings tied to specific seasonal promotions. The McChicken, on the other hand, is a staple item and not offered only during the summer. The Shamrock Shake stands out due to its seasonal availability and the excitement it generates among customers, making it the correct choice for a product associated with limited-time summer offerings.