某程序将256×256的矩阵置初始值0。现假定分给这个矩阵的内存块为1页,页面大小为每页256个整数字。矩阵按行存放,开始时内存为空。若有关变量已放在内存其他处,并常驻内存,且如下编制: VAR A:ARRAY[1…256,1…256]OF INTEGER FOR I:=1 TO 256 FOR J:=1 YO 256 A[I,J]:=0;则程序运行完毕共发生多少缺页中断()。
【简答题】Before the first non-stop flight made in 1949, it ________ necessary for all planes to land for refueling. A) would be B) has been C) had been D) would have been