问题如下：
When accounting standards require recognition of an expense that is not permitted under tax laws, the result is a:
选项：
A. deferred tax liability.
B. temporary difference.
C. permanent difference.
解释：
C is correct.
Accounting items that are not deductible for tax purposes will not be reversed and thus result in permanent differences.
解析：对于一笔费用，会计上要求确认，但是税法上不允许确认，这个是永久性差异。
今天多交的税将来也不会因为这笔费用在tax reporting上可以确认而少交，因为tax reporting是不确认这笔费用的，现在不行，将来也不行，因此是永久性差异，选项C正确。
坏账准备，应该也是属于题干所讲的。那由于坏账准备所造成的属于dtl么?
