should the reliance on another species reach a level so great the organisms are interdependent, scientists consider them to
be symbiotic, or having a prolonged association that is necessary for the continued existence of either one or both.
여기서 should 가 왜 맨 앞에 왔는지 설명해주실 분 있으신ㄱㅏ요 ㅠㅠ 의문문이 아닌데 문장 앞에 올 때 뭐가 생략 된 건가요??