Complex sentence: The D train is directly connected from the Grand Street station in Manhattan's Chinatown to this rapidly growing Chinese enclave between 18th Avenue and 25th Avenue, and it is becoming a third extension of Manhattan's Chinatown.
Split into simpler sentences: The D trains happen to be directly connected from the Grand Street station in Manhattan's Chinatown to the D train stops in this growing Chinese enclave between 18th Avenue and 25h Avenue. It is becoming a third extension of Manhattan's Chinatown.