Centering a \framebox

Centering a \framebox

Before asking, I have checked Centered box, text inside it flushed right?,
Questions about \fbox, and Any way to center text within a \parbox?.
Here I have tested various centering methods (my intention is to use
\centering only) on \framebox and \makebox alike.
\framebox{This is a sentence of text.}\par
\makebox{This is a sentence of text.}\par
{\indent \centering\framebox{This is a sentence of text.}}\par
{\indent \centering\makebox{This is a sentence of text.}}\par
\framebox{\centering This is a sentence of text.}\par
\makebox{\centering This is a sentence of text.}\par
\framebox[5cm]{\centering This is a sentence of text.}\par
\makebox[5cm]{\centering This is a sentence of text.}\par
\framebox[\linewidth]{This is a sentence of text.}\par
\makebox[\linewidth]{This is a sentence of text.}\par
\framebox[5cm]{\centering This is a sentence of text.}\par
\makebox[5cm]{\centering This is a sentence of text.}\par
\framebox{\centering\parbox{5cm}{This is a sentence of text.}}\par
\makebox{\centering\parbox{5cm}{This is a sentence of text.}}\par
\parbox{5cm}{\centering\framebox{This is a sentence of text.}}\par
\parbox{5cm}{\centering\makebox{This is a sentence of text.}}\par
\begin{center}
\framebox{This is a sentence of text.}\par
\makebox{This is a sentence of text.}
\end{center}
The only standard LaTeX method (no packages) I can achieve is using the
center environment (the last one). Is that so, and why?
An image is shown below.