①铅蓄电池充电时是将电能转化为____能

②铅蓄电池放电过程中，反应的化学方程式为  Pb+PbO₂+2H₂SO₄═2PbSO₄+2H₂O，据此可知，铅蓄电池在放电时，溶液的pH不断____（填“增大”、“减小”或“不变”）

③从材料分类角度看，塑料是一类____材料． （填“合成”或“复合”）

④废硫酸直接排放会污染环境，可以用熟石灰中和硫酸，写出该反应的化学方程式____．

因式分解：x²﹣9=____．

    Last summer, Tina's parents needed to work in another city for a month. And Tina had to stay 1 Aunt Betsy in California.

    Tina never saw Aunt Betsy before, 2 she was a little nervous(紧张的). Aunt Betsy told her the 3 in California was hot, so Tina put some shorts and T-shirts in her bag. She 4 put some books in her bag because she enjoyed reading. Her favorite 5 were about horses(马).

    When the 6 came, Aunt Betsy picked up(接) Tina. On the way to Aunt Betsy's house, Tina 7 many horses in the fields(牧场). Tina liked 8 very much and she wished she could have a horse some day.

    When they 9  Aunt Betsy's house, Tina saw a big picture on the wall. It was about a tall brown 10! Aunt Betsy was in the 11, and she was sitting on the horse.

    “Do you 12  the horse? Her name is Lucky. Usually, I visit her 13 a week, every Saturday afternoon for an hour. We can go 14 together this weekend,” said Aunt Betsy.

    Tina felt 15 because her aunt and she had the same hobby. It was going to be a wonderful holiday.