单选题
16.Firms that use computers have found that the number of staff______ is needed for quality control can be substantially reduced.
【正确答案】
D
【答案解析】此句中，found后的that引导的是宾语从句，从句中的“is needed for quality con-trol”解释说明了“staff”，所以应为同位语从句，而引导词只能是that。故答案为D。