Which HTML should you use?

You are developing a customer web form that includes the following HTML.
<input id = “txtValue” />
A customer must enter a value in the text box prior to submitting the form.
You need to add validation to the text box control.
Which HTML should you use?

A.
<input id=”txtValue” type=”text” required=”required”/>

B.
<input id=”txtValue” type=”text” pattern=”[A-Za-z]{3}” />

C.
<input id=”txtValue” type=”required” />

D.
<input id=”txtValue” type=”required” autocomplete=”on” />

Explanation:

Reference:
http://www.w3schools.com/html5/att_input_required.asp