This question examines the understanding of marketing strategies and the role of multiple marketers on a platform. The correct answer is C, as the presence of other marketers on a site like BabyCenter enhances its credibility and objectivity by presenting a wide range of products and viewpoints. Option A is incorrect because including other marketers actually increases the site's objectivity. Option B is incorrect as it contradicts the idea that a variety of products is beneficial. Option D is incorrect because the site's purpose is not to focus solely on the host company's products but to offer a broader range of options.