Fill in the blank with appropriate preposition from the options given below.
'A fair little girl sat ________ a tree.'

The correct answer is Option B (under).

Key Points:
• Concept: Prepositions of Place. 'Under' denotes a position lower than or directly below something.
• Explanation: Sitting beneath the shade/branches of a tree is expressed using the preposition 'under'. The complete natural expression is 'sat under a tree'.
• Other Options: 'over' means directly above; 'into' indicates motion towards the inside; 'with' implies accompaniment, none of which fit logically.
• Official Key: Option 2 ('under') is the official correct answer.
• Key Takeaway: Remember: Use 'under' when indicating a location directly below or beneath an object like a tree.