; and (iv) the financial soundness and credit history of the entity. (C) Security features The Secretary shall ensure that any financing for the project has appropriate security features, such as a rate covenant, supporting the project obligations to ensure repayment. (D) Rating opinion letters (i) Preliminary rating opinion letter The Secretary shall require each entity to provide, at the time of application, a preliminary rating opinion letter from at least 1 rating agency indicating that the senior obligations of the project (which may be the Federal credit instrument) have the potential to achieve an investment-grade rating. (ii) Final rating opinion letter The Secretary shall require each entity to provide, prior to final acceptance and financing of the project, final rating opinion letters from at least 2 rating agencies indicating that the senior obligations of the project have an investment-grade rating. (2) Proposed project The Secretary shall ensure that any common carrier trunk pipeline constructed or increased under this section has, or is increased to, an external diameter of not less than 30 inches. (e) Selection of projects (1) In general In carrying out the program under subsection (a), the Secretary may not provide a secured loan to finance more than one common carrier trunk pipeline project the majority of the pipeline length of which will be constructed in a single census region. (2) Census region defined For purposes of this section, the term census region means 1 of the 4 census regions (northeast, south, midwest, and west) that are designated as census regions by the Bureau of the Census as of the date of enactment of this Act. (3) Priority In carrying out the program under subsection (a) for projects described in (c)(1), the Secretary shall give priority to applications that propose construction of a common carrier trunk pipeline project in an area where pipelines or other linear infrastructure already exist. (f) Secured loans (1) Agreements (A) In general Subject to paragraphs (2) and (3),