等比数列{an}的前n项为Sn,S4=20,S8=30,则S12为______.

题型:填空题

问题:

等比数列{an}的前n项为Sn,S4=20,S8=30,则S12为______.

考点:等比数列的前n项和
题型:填空题

下列有关元素周期表的说法不正确的是:

A.第一张较完善的元素周期表是俄国化学家门捷列夫绘制的

B.元素周期表中的前20号元素属于短周期元素

C.元素周期表主族元素的最外层电子数等于其主族序数

D.由元素在周期表中的位置可以推导该元素可能具有的化学性质

题型:填空题

(10分)已知海王星和地球的质量比M:m=16:1,它们的半径比R:r= 4:1,求:

(1)海王星和地球的第一宇宙速度之比?

(2)海王星和地球表面的重力加速度之比?

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经常使用在道路、广场和施工现场照明的灯是()。

A.高压水银灯

B.卤钨灯

C.荧光灯

D.白炽灯

题型:填空题

The doctor-patient relationship is one of the (1) relationships in life, but many people say this relationship is beyond (2) . Can this relationship be saved The answer is (3) yes, because it must. And if that is lost, medicine becomes a technology and is (4) . In part the crisis in medicine began with doctors (5) themselves from patients.
The more critical work of a doctor happens in the taking of the human (6) . (7) is the most important and most difficult single transaction. The studies show that (8) of all the valuable information that leads to correct diagnosis comes from the history. Another (9) comes from the physical examination, 10% comes from simple (10) tests, and 5% comes from all the complex (11) . So listening is vital, because listening is not merely listening, but to establish a (12) .
But some doctors think listening is (13) . They like to use complex and costly (14) , and use (15) that create adverse reactions and require (16) . They don’t like to listen. Because there’s no premium on listening and that there’s no (17) for listening.
Even so, the doctor-patient relationship is not (18) saving. Because people may ask, what is good health And good health begins first and foremost with (19) . If you don’t care for a (20) , be somebody else, but don’t be a doctor!

题型:填空题

砌筑多孔砌块和密实砌块用砂浆的强度公式有何不同,为什么?

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