![](https://lstatic.shangxueba.com/jiandati/h5/images/m_q_title.png)
Which of the following sentence is NOT appropriate to be the beginning one of a summary ?
A、This paper reports an empirical study on _____.
B、This report focuses on the problem of _______.
C、This article is mainly about ________________.
D、Once upon a time, there was _________________.