Feedback must be completed if and only if Email and password is matched?

I am sending the feedback links which need to be opened if students (whose email id is auto-filled in "Email" box) enter the password. 

I am unable to add the Password field and the condition for Email and Password fields as matching condition?

If I understood you correctly, you want to send your students links that will lead to your form. When they get to the form they will have to type in their password and if it matches their email and password the form will be shown to them. 

To achieve this you will have to create a condition for each email/password pair. I would suggest you if you can, to use one password that you will share with your students since this way of creating conditions will be very hard to implement and maintain.

Let us know if you need more information.