单选题 Some of his suggestions had been rejected ______ they were not practicable.
A. as B. when C. until D. if

【正确答案】 A
【答案解析】他的一些建议因为不可行而被拒绝了。as表原因“因为……”；when为“当……”；until表“直到”；if为“如果”。