Read the text. What is missing in gap C?

• and from the sea has been firmly ensured
• which is a former royal countryside residence
• who designs many royal residences in Europe
• and then rebuilt in the baroque style in the 18th century
• who wanted to decorate the main entrance with waterfalls
• that are located in the park on the coast of the Gulf of Finland
• and on the other hand, to become a monument to Russia’s struggle