Wrap each 3 items with HTML Wrapper code in ForEach loop C#

I need to build an HTML code structure in C# code behind. The code inserted an HTML item that occupies 3 columns in a 12 columns Row (I'm using Zurb Foundation).

I iterate over over a collection of items in a foreach loop.

I want to add a <div class='row'>[item html code here]</div> code that will wrap the 3 column items.

Item code is something like this:

<div class='column large-4 medium-4- small-12' >some content</div>

What logic should I use (C#) in order to be able to inject the item HTML code inside the row code every three items?

My complications start when I need to separate the opening tags (<div class='row'>) with the closing tag (</div>) and put the items codes (the column divs) inside.

Assume large number of items that needs to iterate over.

The results html should look something like this if for example I have 7 items:

<div class='row'>
 <div class='column large-4'>item 1</div>
 <div class='column large-4'>item 2</div>
 <div class='column large-4'>item 3</div>
</div>
<div class='row'>
 <div class='column large-4'>item 4</div>
 <div class='column large-4'>item 5</div>
 <div class='column large-4'>item 6</div>
</div>
<div class='row'>
 <div class='column large-4'>item 7</div>
</div>