Explanation
The correct word to fill in the blank is C: For.
The complete sentence is "Sham is sleeping for ten hours." In this sentence, the word "for" is a preposition that is used to indicate the length of time that Sham is sleeping.
Option A, "since," would not be appropriate in this context because it indicates a starting point or time, which is not relevant to the length of time that Sham is sleeping. Option B, "by," would not be appropriate either because it indicates a deadline or completion time, which is not relevant to the sentence. Option D, "till," would imply that Sham is sleeping until a particular time, which is not what the sentence is trying to convey.
Therefore, the correct preposition to use in this sentence is "for," making the complete sentence "Sham is sleeping for ten hours."
