在等比数列$\left\{a_n\right\}$中,$a_1=-16,a_4=8$则$a_7=$ (       )

英译汉

如图，Rt△ABC中，∠C=90°，D是AC边上一点，AB=5，AC=4，若△ABC∽△BDC，则CD=（　　）

   Why do we come to school? Most of us may say we come to school to study. But to study needs a right way, or you either waste the time or the money. The following are the ways for studying.
    The best time for reading is morning. In the morning the air is fresh and the mind is clear. For that reason we can get good results.
In studying we must have patience（耐心）. If we have not known a text well, we must read it again. We should not read the next one until we have learned the first one well.
   When we are studying, we must put our hearts into the books, or we can get nothing from the books while we are reading.
We must always ask “whys”. If it is not well understood, write it down and ask our teachers or our parents, brothers or friends. In any possible way, we must know it completely and what we have learned can be used well and made better.
   Though there are many ways for studying, yet what I have said above will be enough if we can keep them in heart and do so.