What type of income can be affected by the net investment income tax?

The correct answer is certain investment income because the net investment income tax (NIIT) specifically targets investment income for individuals with income exceeding certain thresholds. This tax applies to net investment income, which includes capital gains, interest, dividends, and rental income (with some exceptions), particularly when the income is generated from investments rather than from active business involvement or wages.

Interest income from bank savings is considered investment income; however, it does not encompass the range of investment returns subject to the NIIT. Wages from employment are not classified as investment income and are therefore outside the scope of the net investment income tax. Rental income on primary residences also does not fall under the NIIT, as it generally considers only rental income from investments in rental properties. Thus, the focus of the NIIT is specifically on earnings derived from certain investment activities, which is why "certain investment income" is the most accurate response.