<p>With has, have, or had, always use the "U" form when possible (swum, begun, run) or the "N" form (written, broken, eaten) or just the "-ed" form when the other options aren't available (worked, hiked, walked). These forms of the verbs are called "Past participles" if you want to research them further for the SAT, which I highly recommend.</p>
<p>Yea you can use both, but I think (not sure) that using "had" is more appropriate when talking about a definite time in the past after some event occured.</p>
<p>But I'm pretty sure that CB was testing for your knowledge of past participles on that one because that type of question frequently appears.</p>