我国走上科技强军之路的标志是____。

小张在家中自制了一个简易密度计并用它来测定盐水的密度．

实验器材有：刻度尺、圆柱形竹筷、细铅丝、烧杯、水、待测盐水。

实验步骤如下：

①用刻度尺测出竹筷的长度L，

②竹筷的下端缠上适量的细铅，

③把自制的密度计放入盛水的烧杯中，静止后用刻度尺测出液面上竹筷的长度h₁（如图所示），

④把自制的密度计放入盛盐水的烧杯中，静止后用刻度尺测出液面上竹筷的长度h_2。

根据上面的你步骤回答下列问题：

  7＋8=（  ）

Dear Lucy,
   We are back in Garden City now. We had    1   good trip.
   I    2  to collect my photos yesterday. They    3great! I showed these photos    4  my classmates. They all   5  them.
   There is a photo of Ben and Simon  6   the Great Wall. There is one of you and  7in the Forbidden City(紫禁城).
We really enjoyed    8vacation. We were sad(悲伤)to   9   you.
   You must   10and visit us in Garden City at Chinese New Year.
                                                                                                                                                          Love,
                                                                                                                                                          Kitty