BEIJING/TAIPEI, March 8 (Reuters) - China said on Wednesday it was "seriously concerned" by Taiwan President Tsai Ing-wen's "transit" plans and had asked Washington for clarification, amid reports she will meet U. China is firmly opposed to any form of official exchanges between the United States and Taiwan, she said, adding: "No one should underestimate the strong determination of the Chinese government and people to safeguard national sovereignty and territorial integrity. See here for a complete list of exchanges and delays