小明体重500N，周末他去“六盘水市游泳馆”游泳，当他套着游泳圈漂浮在2m深水区休息时（游泳圈的重量忽略不计），他所受的浮力为　____ 　N，此时由于不小心，手牌滑落，沉到池底，则手牌受到的液体压强为　____ 　Pa．然后他潜入水中老手牌，从他完全潜入到捞到手牌的过程中，他受到的浮力____ （选填“变大”、“变小”或“不变”）．小明捞到手牌后，若他受到的浮力等于500N，在不做任何动作的情况下，他将在水中____ （选填“上浮”、“下沉”或“悬浮”）．

在我国南海某处打捞了一艘古代沉船，在船中发现了大量的白瓷、青花瓷、彩瓷和珐琅彩等瓷器。根据这一考古发觉材料推断这一沉船事件大致发生在

    There will be many changes in our life in the future. We will____ flying cars to work. We will travel to ____ . Maybe we will ____ live in space. Students won't ____  schoolbags to go to school any more. They will learn on ____ at home. And there will be robots in our home. The robots will help us do all the housework. Life will be great at that time.