12
(A)The fundamental challenge for us all is to change the way we live.
(B)Nearly every drop of water that flows downstream is already allocated.
(C)But the testimony of tree rings shows that those years were much wetter than the long-term historical average.
(D)Scientists change their minds as the evidence they gather becomes more precise and more conclusive.

11 The Colorado River basin水盆, 一盆, 區域, 流域 itself—some 240,000 square miles平方英里 across the West and South West—has experienced經驗豐富  staggering驚人 population growth.

Precipitation雨, （尤指雨或雪的）降落；降水 patterns方式 are changing, in part because of global warming, and the spring春季 run off突然跑掉；迅速離開 from snowpack積雪場 in the mountains takes place earlier than it used to, which means that less water is stored for later in the season. 

12 That means that the only new water source for residential居民區 and commercial growth is water that has been allocated分配；分派 to agriculture.

(A)The fundamental基礎 challenge for us all is to change the way we live. 
(B)Nearly every drop off入睡, 下降 water that flows移動, （尤指液體、氣體或電）流動 downstream順流（地），向下游 is already allocated分配；分派. 
(C)But the testimony（尤指法庭上的）證詞 of tree rings shows that those years were much wetter潤濕 than the long-term historical average. 
(D)Scientists change their minds as the evidence they gather becomes more precise精確 and more conclusive無可置疑.