Halcyon (A):

Meaning: Calm, peaceful, and happy.
This word fits well but isn't as specific to rural or natural settings as some other options.

Perennial (B):
Meaning: Lasting or existing for a long or apparently infinite time; enduring or continually recurring.
This word doesn't quite match the context of describing a type of scene.

Bucolic (C):
Meaning: Relating to the pleasant aspects of the countryside and country life.
This word is perfect because it directly relates to peaceful, rural scenes like hills and valleys.

Eclectic (D):
Meaning: Deriving ideas, style, or taste from a broad and diverse range of sources.
This word doesn't fit the context of describing a specific type of scene.

Quiescent (E):
Meaning: In a state or period of inactivity or dormancy.
While this word can imply calmness, it doesn't specifically relate to the pastoral or rural nature of the scene.

The most fitting word for the blank is bucolic (C).