问题
单项选择题
______ have been made for nearly three decades to increase the amount of precipitation from clouds by seeding them with salt or silver iodide.
A．Devices
B．Hypotheses
C．Attempts
D．Commissions
答案
参考答案：C
解析：[分析]名词辨析 A．Devices装置，设计，策略，设备；B．Hypotheses臆测，假定；C．Attempts努力，尝试，企图；D．Commissions委任，代办(权)，佣金；本题讲的是：已做了近三十年的尝试，试图在云层中加入盐或碘化银来增加降雨量；因此C为答案。