题目

下列金属中，遇到盐酸或强碱溶液都能放出氢气的是（    ） A.  Cu        B.  Mg           C.  Fe             D.  Al 答案：D13．You have two eyes and they are set close together on the front of your face．Have you wondered why？The reasons are simple and important to the way you see the rest of your world． Your eyes are like two small cameras．A camera catches an image of an object and records it on film．Similarly，when you look at something，each eye takes in what it sees and sends this image to the back of the eyeball．Because your eyes are set close together，they view the world from about the same height but from slightly different angles．Working as a team，the eyes send the images to your brain，which puts them together into a single，centered image． Seeing in stereo means seeing with two eyes working together，which is called stereoscopic sight．This allows you to view the world in three dimensions，or 3-D．Seeing depth helps you to judge the distance between you and the objects you see and to adjust to the changing angle at which you see something as you move closer to or farther away from it．If images are coming from only one eye，however，only two of these dimensions----height and width----can be perceived．A world seen with one eye is thus two-dimensional，as in a photograph．Now consider why your two eyes are on the front of your face．Think of other animals with the same arrangement．They are all animals that hunt，like lions and wolves．Their eyes face directly in front of them．This provides a field of sight about 180 degrees wide，which is called binocular（双眼的） sight．On the other hand，animals that are hunted have eyes on the sides of the head，which provides nearly360-degree field of sight．In order to stay alive，they need to see things coming from the sides and from behind．However，without stereoscopic sight，they have difficulty determining how far a danger is． With sight both stereoscopic and binocular，humans share with animal hunters the ability to see from side to side and to accurately determine the distance．If you think it would be great to have another type of sight，perhaps with hundreds of tiny eyes like many insects do，think again!Each tiny insect eye sees only a tiny part．Besides，what if you needed glasses？Be glad for the eyesight that you have．67．According to the passage，the similarity of an eye and a camera is that they bothB．A．can imagine objects               B．can record imagesC．provide centered images           D．work at the same height68．Stereoscopic sight is a result of havingA．A．two eyes close to each other that work togetherB．hundreds of eyes，all seeing tiny parts of an imageC．a three-hundred-sixty-degree field of sightD．one eye on either side of the head，each seeing a different image69．What is the meaning of the underlined word"perceived"in Para3 most similar to？BA．known         B．seen         C．taken            D．understood70．We can infer from the last paragraph thatD．A．our eyes work like camerasB．animal hunters are glad for the sight they haveC．the three dimensions are depth，height and widthD．human beings are fortunate to have such eyesight．