The correct answer is D. non-governmental organization.
An NGO is a non-profit, non-governmental organization that is organized independently from the government. NGOs can be involved in a wide range of activities, including humanitarian relief, environmental protection, and human rights advocacy.
Option A, non-governmental office, is incorrect because an NGO is not an office. An NGO is an organization.
Option B, national-geographical organization, is incorrect because an NGO is not a national-geographical organization. An NGO can be involved in a wide range of activities, not just those related to geography.
Option C, national-governmental organization, is incorrect because an NGO is not a national-governmental organization. An NGO is an organization that is independent from the government.