如图示表示某农作物品种①和②两个品种培育出品种⑥的可能方法，请回答：

已知数列{a_n}中的前n项和为S_n= $\frac{n^2+n}{2}$ ，又a_n=log₂b_n．

假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。
增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。
删除：把多余的词用斜线（＼）划掉。
修改：在错的词下划一横线，并在该词下面写出修改后的词。
注意：1．每处错误及其修改均仅限一词；2．只允许修改10处，多者（从第11处起）不计分。
    My high school life has made me learn many things. Between them teamwork is the most significantly for me. In fact, I didn't realize its importance after I was elected monitor. In the begin, I did almost all the duties myself, however, others students cared little about class activities. Therefore, I worn out and depressed. Then I turned to my head teacher but he advised me to cooperate with others. Gradually, I realized the strengths of my classmates and managed to have everyone to play a part in class. It is working in teams instead of on my own which has freed me of trouble and make my work more efficient.

以下事例中，属于凝固现象的是（   ）

某电器超市销售每台进价分别为200元，170元的A、B联众型号的电风扇，表中是近两周的销售情况：

销售时段	销售数量		销售收入
	A种型号	B种型号
第一周	3台	5台	1800元
第二周	4台	10台	3100元

（进价、售价均保持不变，利润=销售收入﹣进货成本）