Rarely ------ seen far from water ?

The sentence "Rarely ------ seen far from water" requires a verb structure that complements the subject "spotted frogs" while maintaining the grammatical consistency of the sentence. The phrase "are spotted frogs" (option D) correctly uses the verb "are," which is the present tense form of "to be." This structure effectively indicates a state of being, where "spotted frogs" are the subject that is rarely observed away from their preferred habitat, which is close to water.

In contrast, option A, "spotted frogs," cannot stand alone as a complete thought. Option B, "spotted frogs have," introduces a verb that suggests possession but does not logically connect to the act of being seen far from water. Option C, "have spotted frogs," is similarly misplaced, as it suggests an action rather than addressing the rarity of the frogs’ location regarding water.

Thus, the use of "are spotted frogs" (D) establishes the correct subject-verb agreement and accurately conveys the intended meaning, making it the best choice for this sentence construction. This structure highlights the infrequency with which these frogs are found outside their aquatic environment.