By Sheila Dang (Reuters) -Twitter Inc faced a skeptical audience as it showcased its advertising opportunities on Wednesday at an event in New York City, three ad agency executives told Reuters, as the social media company’s plans under billionaire Elon Musk remain unclear. The Tesla chief executive, who is buying Twitter for $44 billion, has tweeted that the platform should not have ads so it can have more control over its content moderation policies. Twitter has told its employees in internal staff meetings and in public filings that its advertising business and other operations would contin…