在驰名中外的北京天坛里，有三处堪称奇观的声学建筑：回音壁、三音石和圜丘．当游客在圜丘顶层的天心石上说话时，听到的声音格外响亮，这是建筑师利用声音的反射，使 ____与原声混在一起，声音得到加强造成的音响效果．

已知关于x的方程x²﹣4x+a=0有两个相同的实数根，则a的值是____．

根据句意及首字母提示完成单词
E____  in our class likes English.
I can't stand this t____ weather.
I don't like lions because they're u____  .
I don't like his new l____ .
Wang Lin is the c____ of the basketball team.
Look! There are a g____  of children on the beach.
The students are taking photos with a c____ .
Her mother is tall and a little bit h____ .
My sister is a n____  in the hospital.
We have many great s____ in the restaurant. 

西瓜甘甜多汁，这些甜美的汁液主要存在于细胞的（　　）