问题如下：
The most likely argument against being concerned about national debt levels is that:
选项：
A. they create disincentives for economic activity.
B. they may finance investment in physical and human capital.
C. they may cause crowding out.
解释：
B is correct.
A proportion of the money borrowed may have been used for capital investment projects or enhancing human capital and these may lead to raised future output and tax revenues.
考点：Limitation of Fiscal Policy
解析： 财政政策所引发的较高负债确实有可能会拖累经济的发展，所以A选项不入选。
如果借债的财政支出是用于了投资，并且投资在了人力资本以及科技方面，那么这会加速一国的经济发展，发展产生的GDP完全足够偿付债务，所以不需要额外担心，因此B选项入选。
扩张的财政政策可能会引起市场利率的上升，阻碍私人部分的投资，这就是所谓的挤出效应，它也是不利于经济发展的。所以C选项不入选。
老师，本题又是against又是concerned是否就是双重否定的意思？
