My teenager son Karl became withdrawn after his father died. As a single parent, I tried to do my best to talk to him. But the more I tried, the more he pulled away. When his report card arrived during his junior year, it said that he had been absent 95 times from classes. In this way he would never graduate. I sent him to the school adviser, and I even begged him. Nothing worked.

    One night I was at work when I got a phone call. A man introduced himself as a head teacher, “I want to talk to you about Karl's absences (缺席).” Before he could say another word I choked up (硬咽), and said sadly, “I love my son. I've tried everything to get Karl to go back to school and nothing has worked. It's out of my hands.” For a moment there was silence on the other end of the line. The head teacher seriously said, “Thank you for your time.”

    Karl's next report card showed a marked improvement in his grades. He was even on the list of the best students at school. In his fourth year, I took part in a parent-teacher meeting. I noticed that his teachers were surprised at the way he had turned himself around. On our way home, he said, “Mum, remember that call from the head teacher last year?” I nodded. “That was me. I thought I'd play a joke but I heard you said. It really hit me how much I was hurting you. That's when I knew I had to make you proud.”

对下列划线词语的解释不正确的一项是(　　)

农民张大爷家又两个大棚，分别种植草莓和西红柿，有关成本和销售情况如表：

（1）2013年，张大爷共销售草莓和西红柿6000千克，获利4万元，求西红柿和草莓各销售多少千克；

（2）张大爷五月上旬和中旬草莓销售额都是5000元，但中旬草莓单价比下旬下降20%，中旬比上旬多销售了100千克，求五月份中旬的销售单价．

（Ⅰ）求家庭的月储蓄y对月收入x的线性回归方程y=bx+a；

（Ⅱ）判断变量x与y之间是正相关还是负相关；

（Ⅲ）若该居民区某家庭月收入为7千元，预测该家庭的月储蓄．

附：线性回归方程y=bx+a中， $\widehat{b}=\frac{{\displaystyle \sum _{i=1}^n{x}_i{y}_i-n\overline{x}\cdot \overline{y}}}{{\displaystyle \sum _{i=1}^n{x}_i{}^2-n\cdot {\overline{x}}^2}}$ ， $\widehat{a}=\overline{y}-\widehat{b}\overline{x}$ ，其中 $\overline{x}$ ， $\overline{y}$ 为样本平均值，线性回归方程也可写为 $\widehat{y}=\widehat{b}x+\widehat{a}$ ．