they surveyed the rich in america and found that the main secret that they could be wealthy was modest spending.이 문장에서they could be wealthy was modest spending
이 부분이 could be 와 was 동사가 두개인데 어떻게 해석하는지 모르겠어요 ㅠㅠ
왜 여기서 동사가 두개가 나온거죠;;