[texhax] The space between different paragraph, the centered part and conjuncted paragraph

[Lian Mo]

Hi:
It is Lian Mo again.

I have two issues and do not know where to change the parameters to solve it.

First, for example

\begin{center} XXXXXXXX \end{center}
YYYYYYY

The space between XXXXXXXX and YYYYYYY is more than the normal double
or single space.

Second,
The space between two paragraphs is more than the normal double or single space.
Also, the space between the TABLE OF CONTENTS and the first content's
line is more than normal space. The space between LIST OF FIGURE and
the first line is more than nomorl space.

It makes the document beautiful, but it is not qualified to my dissertation.

I use the report class style for my dissertation. Where can I find the
related part and change the parameters so that the above spaces are
exactly the same as double or single space.

Thanks!

Lian Mo