The purpose of (66) is to enlarge the (67) , the set of addresses a program can utilize. For example, it might contain twice as many addresses as main memory. A program using all of it, therefore, would not be able to fit in main memory all at once. Nevertheless, the computer could execute such a program by Copying into main memory those portions of the program needed at any given point during execution.
To facilitate copying (66) into real memory, the operating system divides it into pages, each of which contains a fixed number of addresses. Each page is stored on a disk until ii is needed. When the page is needed, the operating system copies it from disk to main memory, translating the (68) into real addresses. The process of translating virtual addresses into real addresses is called (69) . The copying of virtual pages from disk to main memory is known as (70) or swapping.

A．drawing

B．mapping

C．picturing

D．scanning

患者男性，65岁，拟行胆囊切除术。该患者患有冠心病(心绞痛)和胃肠炎。查体：心率104次/分、心律不齐、血压170/110mmHg，心电图提示：ST段改变。空腹血糖12.8mmol/L、血清总胆固醇10.0mmol/L、血清钾3.5mmol/L。

哪一项不是导致冠心病的危险因素()

A．高血压

B．糖尿病

C．家族史

D．高胆固醇血症

E．胃肠炎