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问题 选择题

真空中两个同种点电荷q1、q2相距一定距离，现固定q1，把q2移到远处，在此过程中，q2受到的库仑力

A．不断增大

B．不断减小

C．始终保持不变

D．先增大后减小

答案

答案：B

题目分析：真空中点电荷之间的库仑力，当把固定，把移到远处，电荷间的距离r增大，所以受到的库仑力不断减小。

故选B

点评：库仑定律的适用条件，即的适用条件是：真空中的点电荷。当两点电荷的电量不变时，它们之间的库仑力与距离的平方成反比。

填空题



I am honored to be here today, (1) Harvard at this celebration of the College Board’s half century of working to promote (2) and equal opportunity in higher education.
Before I say anything else, I want to thank everyone in the room for the work you do every day to make college (3) , available, and (4) for millions of young people across the country.
I want to focus my remarks on a matter of (5) to American familiesand to the future of the nation -- restoring education to its proper role as a (6) to equal opportunity and (7) in our society.
This has been an (8) in higher education, with great and creative efforts made by many institutions. Earlier this year, we announced a new (9) at Harvard aimed at the students from families of low and (10) income. Under our new program, families with incomes of (11) will no longer be expected to contribute to the cost of attending Harvard for their children. Families with incomes of less than $ 60,000 will also see their (12) reduced.
We are proud of this effort at Harvard, but we are aware that the programs of individual institutions with means can never be a substitute for our shared (13) to provide adequate funding for Pell grants and other financial aid, and for the state and community college systems that make higher education (14) and affordable for the (15) .
There is something empty about (16) initiatives that may be right for one institution without attention to their broader impact. (17) , we (18) if we urge changes in national policy without doing what we can on our own campuses.
In this spirit, I want to (19) today a problem that is emerging with (20) in this nation.
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我国禁止土壤入境。 ( )
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