A general obligation (GO) municipal bond is backed by the full faith and credit of the issuing municipality or governmental unit, which is why choice C is correct. In practical terms, this means the issuer pledges its general taxing power and overall resources to meet debt service---interest and principal payments. GO bonds are typically supported by the issuer's ability to levy taxes (often property taxes, subject to legal limits), making their repayment source broader than that of revenue bonds.

Choice D describes a revenue bond, which is payable only from a specific revenue stream (e.g., tolls from a bridge, fees from a water/sewer system, or revenues from an airport). Revenue bonds do not rely on the issuer's general taxing power; instead, bondholders depend on the project's or enterprise's revenues. That is a key GO vs. revenue distinction tested heavily on the SIE.

Choice A is incorrect because municipal securities customarily include a legal opinion addressing validity and tax status, especially for tax-exempt issues; the presence of a legal opinion is not something GO bonds uniquely lack. Choice B is incorrect because many municipal bonds, including many GO bonds, are federally tax-exempt on interest (and may also be state/local tax-exempt for in-state residents), though there are exceptions such as taxable munis and AMT considerations in certain cases. The question's best, universally correct feature of a GO bond is the backing by the issuing jurisdiction's full faith and credit.

This question aligns with SIE product knowledge of municipal securities, including repayment sources and how those sources affect credit considerations.