填空题 His recommendation that Air Force {{U}}investigates{{/U}} the UFO sighting {{U}}was{{/U}} approved {{U}}by the commission{{/U}} and referred {{U}}to{{/U}} the appropriate. A. investigates B. was C. by the commission D. to
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【正确答案】 1、A应改为(should)investigate。    
【答案解析】[解析] 同位语从句修饰recommendation，从句用虚拟语气。