question: What is the purpose of the geostationary orbit satellites in the BeiDou-2 system ?
answer: for backward compatibility with BeiDou-1
turker_answer: The purpose of the geostationary orbit satellites in the BeiDou-2 system is for backward compatibility with BeiDou-1 .
rule-based: The purpose of the geostationary orbit satellites in the BeiDou-2 system is for backward compatibility with BeiDou-1 .