计算：-4+7-4=____ ．

   When it rains, do your shoes get wet? Of course they do! But you can buy these pretty red and white “Umbrella for Shoes”. They keep the rain off wet.
   Who sweeps the floor at your home? Do you do it yourself? Perhaps your mother does it. Well, now you just need a cat. Get a cat and buy these four “Dusters (抹布)for Cats ”.
   You talk too long on the phone, don’t you? Most teenagers do! Save time – buy the “Telephone Dumb–bell (哑铃)”! It weighs five kilos. Then your calls will be less than five minutes.
   Do your friends sometimes come up behind you and make you jump? Do cars come around the corner when you try to cross the road? Well, you can solve that problem with these modern “Forward – backward Glasses.” Look forward with the right eye and back with the left.