正确答案: A

各导联均可见P波，P波在Ⅰ、Ⅱ、aVF、V5、V6导联应直立，在aVR导联应倒置，PR间期应0.12秒

题目：窦性心律的心电图表现必须具备

解析：

53．答案：A

[考点] 窦性心律心电图特征

[分析] 窦房结是心脏正常窦性节律的起搏点，冲动在窦房结形成后，先传至右心房，然后经房间束传入左心房。由于心房除极波 (P波)的除极瞬间综合向量总是自右上向左下方向扩展，因此在其除极开始处(右上)放置电极(aVR导联)其P波方向总是向下的(倒置)，在其除极方向处(左下)放置一电极(Ⅰ、Ⅱ、aVF导联)，其P波方向总是向上的(直立)；窦房结发出的冲动经心房传至房室交界区，再经希氏束、束支、浦肯野纤维至心室肌，完成一次心动周期，由心房传至心室，最快传递速度须在0.12秒及以上，故PR间期应0.12秒。

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举一反三的答案和解析：

[单选题]社会保障制度的核心内容是（ ）

社会保险

解析：我国的社会保障体系主要包括社会保险、社会救济、社会福利、优抚安置等方面。其中，社会保险是社会保障体系的核心部分，社会福利是社会保障的最高层次，社会救济是社会保障的最后防线。

[单选题]我国婚姻法规定，“子女可以随父姓，也可以随母姓”。这一规范属于

任意性规范

[单选题]Text 3When it comes to the slowing economy, Ellen Spero isn’t biting her nails just yet. But the 47-year-old manicurist isn’t cutting, filling or polishing as many nails as she’d like to, either. Most of her clients spend $12 to $50 weekly, but last month two longtime customers suddenly stopped showing up. Spero blames the softening economy. “I’m a good economic indicator,” she says. “I provide a service that people can do without when they’re concerned about saving some dollars.” So Spero is downscaling, shopping at middle-brow Dillard’s department store near her suburban Cleveland home, instead of Neiman Marcus. “I don’t know if other clients are going to abandon me, too” she says.

Even before Alan Greenspan’s admission that America’s red-hot economy is cooling, lots of working folks had already seen signs of the slowdown themselves. From car dealerships to Gap outlets, sales have been lagging for months as shoppers temper their spending. For retailers, who last year took in 24 percent of their revenue between Thanksgiving and Christmas, the cautious approach is coming at a crucial time. Already, experts say, holiday sales are off 7 percent from last year’s pace. But don’t sound any alarms just yet. Consumers seem only concerned, not panicked, and many say they remain optimistic about the economy’s long-term prospects, even as they do some modest belt-tightening. Consumers say they’re not in despair because, despite the dreadful headlines, their own fortunes still feel pretty good. Home prices are holding steady in most regions. In Manhattan, “there’s a new gold rush happening in the $4 million to $10 million range, predominantly fed by Wall Street bonuses,” says broker Barbara Corcoran. In San Francisco, prices are still rising even as frenzied overbidding quiets. “Instead of 20 to 30 offers, now maybe you only get two or three,” says john Deadly, a Bay Area real-estate broker. And most folks still feel pretty comfortable about their ability to find and keep a job. Many folks see silver linings to this slowdown. Potential home buyers would cheer for lower interest rates. Employers wouldn’t mind a little fewer bubbles in the job market. Many consumers seem to have been influenced by stock-market swings, which investors now view as a necessary ingredient to a sustained boom. Diners might see an upside, too. Getting a table at Manhattan’s hot new Alain Ducasse restaurant need to be impossible. Not anymore. For that, Greenspan & Co. may still be worth toasting. 第51题：By “Ellen Spero isn’t biting her nails just yet”(Line 1, Paragraph 1), the author means

Spero is not in a desperate situation.