Choice "D" is correct. When an auditor believes that there is substantial doubt about an entity's ability to continue as a going concern, the auditor is required to consider management's plans for dealing with the conditions or events that led to the auditor's belief, including:

1. Plans to borrow money or restructure debt

2. Plans to sell assets

3. Plans to delay or reduce expenditures

4. Plans to increase ownership equity

Choice "b" is incorrect. Making a decision to purchase rather than continue leasing would generally not be a mitigating factor for the concern over whether a company can continue as a going concern.Choice "a" is incorrect. Making a decision to pay cash dividends would generally not be a mitigating factor for the concern over whether a company can continue as a going concern.
Choice "c" is incorrect. Making a decision to increase the useful life estimate of capital assets would not be considered a genuine mitigating factor for the concern over whether a company can continue as a going concern. In fact, it would likely concern the auditor that the management was trying to cover up their financial results through the use of an unreasonable estimate.