The Japanese car, which is more economical, has long been considered a______to US car makers.
【正确答案】 D
【答案解析】解析：本题考查compete各种词性的辨析。因为需要填名词，所以先排除选项A和B。competition，竞争；competitor，竞争对手。因为是与后面的maker相比较，所以用competitor更合适，故答案选D。