In certain cases, some small states accept the protection of other states without destroying their sovereignty. Such arrangements exist for Liechtenstein (as stated above), Monaco (under the protection of France by the 1918 treaty between Monaco and France), and San Marino (under the protection of Italy). The States in this category, though under the protection of other states, are not protectorates in the sense the term is associated with the underdeveloped and exploited territories. Therefore, the correct option is D.