Attemptshavebeenmadefornearlythreedecadestoincreasetheamountofprecipitationfromcloudsbyseedingthemwi

参考答案:

C

名词辨析。attempt努力，尝试：abandon the attempts放弃尝试。device装置：a device for opening bottles一个打开瓶子的装置。hypothesis假设：This is only a sort of scientific hypothesis which has not been proved by experiments．这仅仅是一个尚未被实验证明的科学假说。efforts努力，尽力：Please put more efforts into your school work．请你在功课上再努点力。