Which of the following types of income is included in investment income?

Investment income consists of earnings derived from investments, rather than from direct employment or service work. Taxable dividends, which are a distribution of a portion of a corporation's earnings to its shareholders, are a prime example of this type of income. When an individual owns stock and receives dividends, those payments represent a return on investment in that company, qualifying them as investment income.

In contrast, salary from employment constitutes earned income, as it arises from labor and services provided. Child support payments are not considered income; instead, they are transfers of wealth meant to support a child, and cash gifts fall into the category of personal gifts rather than earned or investment income. Thus, taxable dividends are the correct answer as they directly correlate with income earned through investments.