Task: Question Generation
Input (English): Background Paragraph: The water level is seasonal, being lowered by about 10 feet (3.0 m) over the winter. The reservoir fills in the spring from snow melt and underground springs. The lake is usually at full level by late spring, but in the occasional years of low snow melt and low rainfall, it may remain up to several feet below its typical level. Water is let out of the lake in the fall so that ice will not damage docks and other structures around the lake. This also leads to excellent water quality, as a significant portion of the water is replaced every year. 
Story: There are two hydroelectric dams in North Dakota. Both of them has large lakes or reservoirs, reservoir A and reservoir B. Since North Dakota has one the lowest unemployment rates in the country, it's hard to find an engineer to regulate and maintain the reservoirs. This year reservoir A could hire an engineer, but reservoir B failed to find an engineer. As a result, there is no one to regulate reservoir B. The engineer for reservoir A let the water out in the fall. But there was no one to do that for reservoir B.
Output (English): In which reservoir a good portion of the water would most likely not be replaced?