As you answer questions about her W-4, it will be helpful to know that:

She is not married and does not have any children.
Jane's parents still claim her as a dependent on their tax return.
Before you answer the following questions, make sure you read the paragraph on the W-4 form titled "Exemption from withholding" including the "Note."

Should Jane enter the number 1 on line C? Why or why not?

Jane should not enter the number 1 on line C of her W-4 form. The reason is that line C is used to claim withholding allowances, which are generally based on the individual's personal and financial situation. In this case, Jane is not married, does not have children, and her parents still claim her as a dependent on their tax return. Since she does not qualify for any additional allowances, she should not enter the number 1 on line C.