方框中所给单词的适当形式填空，使对话通顺、正确。每词仅用一次（每空一词）。

Sandy: Mom, I'm really worried.

Mom: Why? What's the ____?

Sandy: I can't find my schoolbag.

Mom: Well, where did you last put it?

Sandy: I can't remember! I ____ a concert yesterday so it might still be in the museum hall.

Mom: Do you have anything ____ in your schoolbag?

Sandy: No, just my books, my pink hair band and some tennis balls.

Mom: So it can't be ____.

Sandy: Oh, wait! I went to a picnic after the concert. I remember I had my schoolbag with me at the picnic.

Mom: So could it still be at the park?

Sandy: Yes. I left early, before the rest of my ____. I'll call them now to check if anybody has it.

一定质量分数的硝酸钾溶液可用做无土栽培的营养液．请通过计算回答：

（1）硝酸钾中钾元素、氮元素、氧元素的质量比是　 ____　．

（2）某蔬菜基地欲配制500kg溶质质量分数为8%的硝酸钾溶液，需要硝酸钾　 ____　kg，水　 ____　kg．

（3）已知在15⁰C时硝酸钾的溶解度为25g，则该温度下硝酸钾的饱和溶液中溶质质量与溶液质量的最简整数比为 ____．