The term 'common culture' refers to cultural elements that are widely shared among a large group of people, often leading to a sense of unity. Option A is correct as it accurately describes this concept. Option B is incorrect because it refers to a niche culture rather than a widespread one. Option C is misleading as common culture is not limited to immigrants. Option D, while partially true, does not capture the essence of what 'common culture' signifies, which is more about shared traits than change.