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【英语模拟题】
19. Not until the dedication of Yellowstone Park in the late nineteenth century ______ a national park.
A. the United States had B. did the United States have
C. when the United States had D. the United States having
20. Academics have claimed that a prototype robot ______ to inspect and pick hard-to-harvest soft fruits is set to be unveiled in time for Brexit.
A. designing B. designed C. to design D. design
