填空题 Geologists (at) the Hawaiian Volcano Observatory (rely on) (a number of) instruments to (studying) the volcanoes in Hawaii. A. at B. rely on C. a number of D. studying
  • 1、
【正确答案】 1、D    
【答案解析】改为study。句中to是不定式短语标志，后应接动词原形。