纳氏试剂比色法测定水中氨氮时，为除去水样色度和浊度，可采用（）法和（）法。
参考答案：絮凝沉淀；蒸馏
一张作文纸共21行，每行18个格子．这张纸一共大约有______个格子．
读问题，再回答。
1. Which season do you like best?
_______________________________________________
2. When's your birthday?
3. What time is it?
4. When do you eat breakfast?
5. What season is it now?
