我们的绿卡在4月底已经批准了，而且收到了。 可今天接到e-mail,说：On July 23, 2010, we mailed a notice requesting additional evidence or information in this case I485
APPLICATION TO REGISTER PERMANENT RESIDENCE OR TO ADJUST STATUS. Please follow the instructions on the notice to submit the requested information. This case will be in suspense until we receive the evidence or the opportunity to submit it expires. Once we receive the requested evidence or information and make a decision on the case, you will be notified by mail. If you move while this case is pending, please use our Change of Address online tool to update your case with your new address or call our customer service center at 1-800-375-5283.
我有些糊涂了，为什么会接到这样的信件，不是已经批准了么？还要什么新材料呢？ 谁能给我解答一下呢？