With the successful launch of Tiangong-I, which was breakthrough in space field, China's space dream took a step closer to reality.
A. a; / B. the; a C. a; the D the; /
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解析：句意：随着航空领域的一大突破天宫一号的成功发射，中国的太空梦朝现实更迈进了一步。第一空填a，泛指这是一个突破，第二空不填，reality是抽象名词，选A。