Final answer:
The sentence 'He is cunninger than his sister' should be corrected to 'He is more cunning than his sister' to use the proper comparative form of the adjective 'cunning.' The sentence 'He is cunninger than his sister' can be rewritten as 'He is more cunning than his sister'. In this rewritten sentence, the comparative form 'more' is used to indicate that the degree of cunningness is higher in the subject compared to his sister. This is the standard way to express a comparative relationship between two objects or individuals in English grammar.
Step-by-step explanation:
The correct comparative form of 'cunning' should use 'more' rather than '-er' because 'cunning' does not typically take the '-er' suffix for its comparative form. Therefore, the sentence should be rewritten as: The sentence 'He is cunninger than his sister' can be rewritten as 'He is more cunning than his sister'. In this rewritten sentence, the comparative form 'more' is used to indicate that the degree of cunningness is higher in the subject compared to his sister. This is the standard way to express a comparative relationship between two objects or individuals in English grammar.
'He is more cunning than his sister.'