Which of the following is not considered a part of external assurance over sustainability reporting, as stated by the Global Reporting Initiative (GRI) Reporting Framework?

a. External assurance engagements should assess the extent to which the report preparer has applied the GRI Reporting Framework in reaching its conclusions.

b. External assurance engagements should be conducted by those with competence in the subject matter and assurance practices

c. External assurance engagements can be issued by the CFO of the company issuing the sustainability report.

d. External assurance engagements should assess whether the sustainability report is reasonable, balanced, and appropriately inclusive