The word "them" in Line 7, Para. 2 refers to _____.
A.doctors who treat heart diseases B.makers of artificial hearts C.America’s health-care programs D.New model of artificial hearts正确答案D
The word "them" in Line 7, Para. 2 refers to _____.
A.doctors who treat heart diseases B.makers of artificial hearts C.America’s health-care programs D.New model of artificial hearts正确答案D