Final answer:
The most likely deductible expense for Dr. Lawrence Lane, a medical professional and sole proprietor, when preparing his tax return in Canada, is business-related travel expenses, as they directly relate to his medical practice.
Step-by-step explanation:
The correct deduction for Dr. Lawrence Lane, a sole proprietor specializing in oncology when preparing his tax return in Canada, would most likely be c. Business-related travel expenses. This is because such expenses are directly related to the operation of his medical practice. Home mortgage interest is not typically deductible for a business unless a portion of the home is used exclusively for business purposes. Childcare expenses are personal and not generally deductible for most businesses. Lastly, student loan interest deductions in Canada are usually only available for the individual's personal income tax and would not be associated with the business expenses of a medical professional.