In April 2018, Dan is audited by the IRS for the year 2016. During the course of the audit, the agent discovers that Dan's deductions for business travel and entertainment are unsubstantiated and a $600 deficiency assessment is proposed for the tax year 2016. The agent also examined some prior year returns. The agent discovers that Dan failed to report $40,000 of gross business income on his 2014 return. Gross income of $60,000 was reported in 2014. The agent also discovers that Dan failed to file a tax return in 2009. Will the statute of limitations prevent the IRS from issuing a deficiency assessment for 2016, 2014, or 2009? Explain.