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问题 选择题
已知函数f（x）=
3x
+1，则
lim
△x→0
f(1-△x)-f(1)
△x
的值为（　　）
A．-
1
3
B．
1
3
C．
2
3
D．0
答案

∵函数f（x）=

3x
+1，∴f′（x）=
1
3
3x2
．

∴

lim
△x→0
f(1-△x)-f(1)
△x
=-1×
lim
△x→0
f(1-△x)-f(1)
-△x
=-f′（1）=-
1
3
．

故选：A．

填空题


The United States counts its population every ten years, and each census reveals that the racial and ethnic mix is changing dramatically, so by the year 2050, the "average" American will not be descended from (1) , but the majority of U. S. residents will trace (2) ancestry to Africa, Asia, the Hispanic world, the Pacific Islands, or the Middle East. Once the United States was a microcosm of European nationalities, (3) the United States is a microcosm of the world. The United States is (4) considered a "melting pot" society by many of its residents. (5) , many people prefer the term "salad bowl." They use this (6) to describe American society. American society will soon be (7) nonwhite. "Melting pot" implies that the different ethnic groups blend together (8) one homogeneous (9) , "salad bowl" (10) that nationalities, like the ingredients in a mixed green salad, retain their cultural (11) . Earlier generations of (12) believed they had to learn English quickly not only to survive but also for (13) .
Now, many immigrant groups do not (14) the same need. Because there are many places in America (15) you can work, shop, get medical care, marry, divorce and die without knowing English. (16) , Chinatown in San Francisco and New York. Also, Los Angeles has many Vietnamese immigrants and immigrants from Mexico. (17) , many immigrant groups want their children to know their (18) culture. Many Hispanics, for instance, want their children to learn (19) English and Spanish and study the Spanish language in school. They are fighting for the (20) to bilingual education in many communities. In many communities they are in the majority.
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多项选择题

人工流产后远期并发症有______

A．空气栓塞

B．宫颈粘连

C．宫腔粘连

D．子宫穿孔

E．人工流产综合反应
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