White smoke __________25～30 meters above the hill as they approached it.
A． has been seen rise
B． had been seen rising
C． was seen rise
D． was seen rising
正确答案：D
本题考查时态及分词用法关于时态主从句时态保持一致应该用一般过去时；关于分词动词rise应该用现在分词的一般式(rising)表示正在进行的动作因此正确答案为D题干意思：当他们靠近时发现滚滚白烟已经越过山头25～30米高了
