问题：
Until the start of the Industrial Revolution, mankind was poor, hungry, and constantly at the _______ of disease and natural disasters．
A.power
B.limit
C.control
D.mercy
Until the start of the Industrial Revolution, mankind was poor, hungry, and constantly at the _______ of disease and natural disasters．
A.power
B.limit
C.control
D.mercy
A.power
B.limit
C.control
D.mercy
参考答案：