【单选题】
            
 Insulin is manufactured by specialized cells in the pancreas and released ______ glucose reaches a certain concentration in the bloodstream.
A.(which
B.(whenever
C.(how
D.(during
        
        
			
            
            
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				根据网考网移动考试中心的统计,该试题:
19%的考友选择了A选项
60%的考友选择了B选项
11%的考友选择了C选项
10%的考友选择了D选项