Final answer:
The sentence 'He was playingthe playground' is incorrect due to a missing preposition. The corrected sentence is 'He was playing on the playground'.
Step-by-step explanation:
The sentence 'He was playingthe playground.' is grammatically incorrect. This sentence is missing a preposition between the words 'playing' and 'the'. The correct preposition to use, from the given options, is 'on'. Therefore, the corrected sentence should read: 'He was playing on the playground'.
Learn more about Prepositions