Designing a cover specifically for an e-book is rare: Most e-book covers are digital images of their print namesakes.
专门为一本电子书设计封面也很少见，大部分电子书的封面都是同名实体书封面的电子版。
Viewers can add comments, keywords and identify people in images in the three sets - Launch/Takeoff, Building NASA, and NASA Center Namesakes, which records historical figures.
图片浏览者能够添加评论，关键词，在三个图集——“发射”、“NASA建设”与“用历史人物命名的NASA宇航中心”上圈人。
Viewers can add comments, keywords and identify people in images in the three sets - Launch/Takeoff, Building NASA, and NASA Center Namesakes, which records historical figures.
图片浏览者能够添加评论，关键词，在三个图集——“发射”、“NASA建设”与“用历史人物命名的NASA宇航中心”上圈人。
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