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    As young students, you have many dreams. These dreams can be very big, such as winning the Nobel Prize; they can also be small, such as becoming one of the best students in your class.Once you find a dream, what do you do with it ? Do you ever try to make your dream real?
    Andrew Matthews, an Australian writer, tells us that making your dreams real is life's biggest challenge. You may think you're not very good at some school subjects, or that it's impossible for you to become a writer. Those kinds of ideas stop you from realizing your dream. In fact, everyone can realize his dream. The first thing you must do is to remember what your dream is. Don't let it leave your heart. Keep telling yourself what you want every day and then your dream will come true faster. You should know that a big dream is, in fact, made up of many small dreams.
    You must also never give up your dream. There will be difficulties on the road to your dreams. But the biggest difficulty comes from yourself. You need to decide what is the most important. Studying instead of watching TV will help you to get better exam results, while saving five yuan instead of buying an ice cream means you can buy a new book.
    As you get closer to your dream, it may change a little. This is good as you have the chance to learn something more useful and find new hobbies.

—What can we do next'?—Let's think ________it．

澄清石灰水长期敞口放在空气中会变浑浊。这是因为空气中含有(   )

生物体的呼吸作用，就是在____的参与下，分解体内的____，释放____供生命活动的需要的过程．吸气时，肺泡内氧的浓度比血液里的____（填“高”或“低”），氧便从肺泡扩散到____里；因此，血液中的氧气含量增加，从这里可以得出：经过肺泡的过程是____血变成____血的过程；而在身体各部分的组织处则刚好相反，血液流经身体的各组织时，氧气被组织的细胞利用，因此血液中的氧气含量下降，所以：血液从____血变成____血．

下面(    )组数，从中任选两个数，这两个数的和是奇数的可能性大。