Dams vary (in size) (from small rock barriers to) concrete structures (many feet) (height).
A. in size B. from small rock barriers to C. many feet D. height

单项选择题Your analogywas not a good one because the two situations are not similar.

单项选择题Until she was 11 years old, Elizabeth Barrett Browning was confinedto her home by her tyrannical father.