A very typical example of a certain person or thing so its D sorry if i get it wrong:)
In this instance, you would use <em>in </em>university. <em>At </em>is only used before specific terms such as "I am studying <em>at </em>Harvard" or "I am studying <em>at </em>Williams College."
For the second question, context must be applied. If you are talking about the corner of a room, <em>in </em>should be used. However, if you are talking about the corner of a sidewalk or street, <em>on </em>or <em>at </em>would be correct.
I hope I helped!
4. Is the best answer because it stays on topic and has a similar tone to the previous sentences.
