Final answer:
The grammatically correct sentence is 'Please submit your expense reports by the end of the day to ensure timely reimbursement.'
Step-by-step explanation:
The grammatically correct sentence is D. Please submit your expense reports by the end of the day to ensure timely reimbursement. In this sentence, the subject 'you' is implied and the verb 'submit' is in the imperative form. The possessive pronoun 'your' correctly indicates that it is your expense reports that need to be submitted. The placement of the words is also correct, with 'expense' modifying 'reports'.
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