选出应填入下面一段英语中______内的正确答案。 Since the time of John von Neumann, the basic conceptual model used to think about computers and programs has (1) unchanged, in (2) of many advances in both hardware and software technology. In the (3) that von Neumann proposed, the basic instruction cycle is for the processor to fetch the instruction pointed at by the program counter, (4) the program counter, and then execute the instruction. Because instructions are executed strictly sequentially, there is little inherent parallelism, and (5) opportunity to employ large numbers of processors to gain speed. 供选择的答案： (1) small    (2) big    (3) add    (4) little    (5) model (6) remained    (7) style    (8) increase    (9) stead    (10) spite (11) already   (12) period   (13) formula    (14) decrease    (15) not