Dec 10 2013 Telecoms move after ratings changes By Sara Sjolin, MarketWatch LONDON (MarketWatch) — European stock markets dropped on Tuesday after a mixed bag of data from China and major euro-zone economies, while speculation about potential tapering in the U.S. also provided an uncertain backdrop. The Stoxx Europe 600 index (STX:XX:SXXP)  lost 0.7% to close at 314.91,…