问题
单项选择题
用谓词来表达查询要求的方式是______。
A．关系演算
B．关系代数
C．关系逻辑
D．关系查询
答案
参考答案：A
解析：关系代数是通过对关系的运算来表达查询要求的方式。关系演算是用谓词来表达查询要求的方式。
搜题请搜索小程序“爱下问搜题”
用谓词来表达查询要求的方式是______。
A．关系演算
B．关系代数
C．关系逻辑
D．关系查询
参考答案：A
解析：关系代数是通过对关系的运算来表达查询要求的方式。关系演算是用谓词来表达查询要求的方式。
| With the understanding of phobias has come a magic bag of treatments: exposure therapy that can stomp out a lifetime phobia in a single six-hour session; virtual-reality programs that can safely simulate the thing the phobia most fears, slowly stripping it of its power to terrorize; new medications that can snuff the brain’s phobic spark before it can catch. In the past year, the U. S. Food and Drug Administration approved the first drug—an existing antidepressant. Most psychologists now assign phobias to one of the three broad categories: social phobias, in which the sufferer feels paralyzing fear at the prospect of social or professional encounters; panic disorders, in which the person is periodically blindsided by overwhelming fear for no apparent reason; and specific phobias—fear of snakes and enclosed spaces and heights and the like. If you are living with a generalized sense of danger, it can be profoundly therapeutic to find a single object on which to deposit all that unformed fear—a snake, a spider and a rat. A specific phobia becomes a sort of backfire for fear, a controlled blaze that prevents other blazes from catching. But a condition that is so easy to pick up is becoming almost as easy to shake, usually without resort to drugs. What turns up the wattage of a phobia the most is the strategy the phobias rely on to ease their discomfort: avoidance. The harder phobics work to avoid the things they fear, the more the brain grows convinced that the threat is real. Progress in treating social-anxiety disorder is also providing hope for the last—and most disabling—of the family of phobias: panic disorder. Panic disorder is to anxiety conditions what a tornado is to weather conditions: a devastating sneaks havoc and then simply vanishes. Unlike the specific phobic and the social phobic who know what will trigger their fear, the victim of panic attacks never know where or when one will hit. Someone who experiences an attack in, say, a supermarket will often not return there, associating the once neutral place with the traumatic event. But the perceived circle of safety can quickly shrink, until sufferers may be confined entirely to their homes. When this begins to happen, panic disorder mutates into full-blown agoraphobia. The treatment for agoraphobia is much the same as it is for social phobia: cognitive-behavioral therapy and drugs. |
Which of the following is NOT true of panic disorder
A．It is the most serious type of phobias.
B．The doctors are getting to know its cause.
C．It will make the sufferers’ safe place become smaller.
D．The doctor can use the experience from social phobia.