How to capitalize first character after dot (.) and first character of string.

user insert like this :-

construct a vector for each answerer based. on the answers that they've written . this

vector can encode what the author knows about .then, when a new question comes in.

wonstruct a vector for each answerer based. on the answers that they've written . this

vector can encode what the author knows about .then, when a new question comes in.

qonstruct a vector for each answerer based. on the answers that they've written . this

vector can encode what the author knows about .then, when a new question comes in

And I want to display like this :-

Construct a vector for each answerer based. On the answers that they've written . This

vector can encode what the author knows about .Then, when a new question comes in.

Wonstruct a vector for each answerer based. On the answers that they've written . This

vector can encode what the author knows about .Then, when a new question comes in.

Qonstruct a vector for each answerer based. On the answers that they've written . This

vector can encode what the author knows about .Then, when a new question comes in

This Is My Code (It also Contain tags):-

string description ="<div><b><u>Construct a vector for each answerer based. On the answers that they've written . This </u></b></div><div><b><u>vector can encode what the author knows about .Then, when a new question comes in.</u></b></div><div><font face=\"georgia\"><br></font></div><div><div><font face=\"georgia\">Wonstruct a vector for each answerer based. On the answers that they've written . This </font></div><div><font face=\"georgia\">vector can encode what the author knows about .Then, when a new question comes in.</font></div></div><div><br></div><div><div><b><i><font face=\"courier new\">Qonstruct a vector for each answerer based. On the answers that they've written . This </font></i></b></div><div><b><i><font face=\"courier new\">vector can encode what the author knows about .Then, when a new question comes in</font></i></b></div></div>"

var sourcestring = description;

var v = new Regex(@"(^[a-z])|[?!.:,;]\s+(.)|[.][a-z]|.(< >)[a-z]", RegexOptions.ExplicitCapture);

var SentanceCasedis = v.Replace(sourcestring.ToLower(), s => s.Value.ToUpper());