[解析]
(1)A.细节理解题。根据第一段最后一句take away floodwater and provide water for 50 cities in the province.(排除洪水,为全省50个城市供水。)可知,都江堰的作用是灌溉土壤和泄洪,故选A。
(2)B.细节理解题。根据第二自然段的最后一句They studied the problem and discovered that the river most often overflowed when winter snow at the top of the nearby Mount Yulei began to melt as the weather warmed.(他们研究了这个问题,发现随着天气变暖,附近玉雷山山顶的冬季积雪开始融化时,河流最常泛滥。)可知,岷江的洪水问题主要是冬天山上的积雪融化导致的,A.Heavy rains大雨;B.Melting snow正在融化的雪;C.Low river banks低河岸;D.Steep(陡峭的) mountains陡峭的山脉。故选B。
(3)C.细节理解题。根据第四自然段的倒数第二句He used a combination of fire and water to heat and cool the rocks until they cracked and could be removed.(他用火和水的结合来加热和冷却岩石,直到它们破裂并被移除。)可知,李冰是用加热石头和用水冷却的方式使石头爆裂成小块,从而移开大石,故选C。
(4)A.推理判断题。根据最后一自然段的最后一句Dujiangyan still lets water flow through the Minjiang River naturally,enabling ecosystems and fish populations to exist in harmony.(都江堰仍然让水自然流过岷江,使生态系统和鱼类种群和谐共存。)可知,都江堰至今都受科学家所推崇是因为都江堰能让水自然地流入到岷江中,并且使生态系统和水生物和平共处,故选A。