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问题 解答题
已知关于x的不等式
ax-5
x2-a
＜0的解集为M．
（1）当a=4时，求集合M；
（2）若3∈M且5∉M，求实数a的取值范围．
答案

（1）a=4时，不等式化为

4x-5
x2-4
＜0，即（4x-5）（x2-4）＜0

利用穿根法解得M=（-∞，-2）∪（

5
4
，2）．

（2）当a≠25时，由

3∈M
5∉M
得
3a-5
9-a
＜0
5a-5
25-a
≥0

∴a∈[1，

5
3
）∪（9，25）；

当a=25时，不等式为

25x-5
x2-25
＜0⇒M=（-∞，-5）∪（
1
5
，5）．

满足3∈M且5∉M，∴a=25满足条件．

综上所述，得a的取值范围是[1，

5
3
）∪（9，25]．

单项选择题

迷走神经节后纤维兴奋引起胃幽门部胃泌素分泌的神经递质是（）.

A.乙酰胆碱

B.三磷酸腺苷

C.蛙皮素

D.一氧化氮
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单项选择题

The most popular organic gem is the pearl. A pearl is the response of a marine mollusk to the presence of an irritating impurity accidentally introduced into its body; a cultured pearl is the result of the intentional insertion of a mother-of-pearl bead into a live mollusk. Whether introduced accidentally or intentionally, the pearl-making process is the same: the mollusk coats the irritant with a substance called nacre. Nacre is composed chiefly of calcium carbonate. Because very few natural pearls are now on the market, most pearls used in fine jewelry are cultured. These include "Biwa" pearls and most other freshwater pearls. Cultured pearls are not easily distinguished from natural pearls except by an expert.

Cultured pearl is formed by________.

A．insertion of a pearl into a live mollusk

B．an oyster into which a piece of grit has been placed

C．putting in a live mollusk

D．placing a bead into culture
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