阿摩線上測驗
21. The most serious health problem ________ infectious diseases. Today, the number one health problem in
the United States is obesity.
(A) was used to be
(B) used to have been
(C) used to be
(D) was used to being
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統計： A(61), B(8), C(237), D(21), E(0) #3089109
統計： A(61), B(8), C(237), D(21), E(0) #3089109
