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　【Paragraph 2】The Ogallala aquifer is a sandstone formation that underlies some 583,000 square kilometers of land extending from northwestern Texas to southern South Dakota. Water from rains and melting snows has been　accumulating in the Ogallala for the past 30,000 years. Estimates indicate that the aquifer contains enough water to fill　Lake Huron, but unfortunately, under the semiarid climatic conditions that presently exist in the region, rates of addition　to the aquifer are minimal, amounting to about half a centimeter a year.(Depletion of the Ogallala Aquifer)

　　Which of the sentences below best expresses the essential information in the highlighted sentence in the　passage? Incorrect choices change the meaning in important ways or leave out essential information.

　　○Despite the current impressive size of the Ogallala aquifer, the region’s climate keeps the rates of water additionvery small.

　　○Although the aquifer has been adding water at the rate of only half a centimeter a year, it will eventually　accumulate enough water of fill Lake Huron.

　　○Because of the region’s present climatic conditions, water is being added each year to the aquifer.

　　○Even when the region experiences unfortunate climatic conditions, the rates of addition of water continue toincrease.