Extracting all data from a list tag using HTML Agility Pack in C#

I am using the HTML Agility Pack to extract data. I want to extract all list items from the source:

<div id="feature-bullets" class="a-section a-spacing-medium a-spacing-top-small">

<ul class="a-unordered-list a-vertical a-spacing-mini">

<li><span class="a-list-item">
some data 1

</span></li>

<li><span class="a-list-item">
some data 2

</span></li>

<li><span class="a-list-item">
some data 3

</span></li>

<li><span class="a-list-item">
some data 4

</span></li>

</ul>

My code so far:

string source = someSource

var htmlDoc = new HtmlAgilityPack.HtmlDocument();
htmlDoc.LoadHtml(source);

How can I extract all the list items to get a result similar to this:

List value 1 is: some data 1
List value 2 is: some data 2
List value 3 is: some data 3
List value 4 is: some data 4

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Author: Josie