________ these pictures, I couldn't help thinking of those days when I was in Beijing and ________ from the top of a thirty-storeyed building, Beijing looks more beautiful. A.Seeing; seenB.Seen; seeingC.Seeing; seeingD.Seen; seen
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A解析该题可从空格前后的逻辑主语确定所需语态，第一空主语是I，第三空主语是Beijing，所以前都用主动形式，后者则需用被动形式。