Linda is a 15-year –old American girl. She is outgoing and likes making friends. Her parents are very   1 .They have no tome to stay with Linda,  2she spends a lot of time on the Internet(网络) every day. She likes  3    with other people on QQ and her QQ name is Lily.
   Last year, Linda got to know a young man on the Internet.  4 name is Mike. Mike is 18 years old. He lives  5  Toronto, Canada. He is very friendly and 6
   He likes to tell jokes and makes Linda happy. Linda talked with him on QQ for long hours every night. A few days later, Mike posted a 7 of himself(他自己) to Linda. He is 8 and good-looking in the photo. Linda likes him very much and they become good friends.
   Last month, Linda’s parents went to Toronto for a meeting (会议). Linda wanted to visit his friend Mike. She asked her parents to  9her there. When Linda arrived at Mike’s house, she found her 10was only a nine-year-old boy .He wasn’t that tall man in the photo. How surprised Linda was!

已知a＞b，ab=2且a²+b²=5，则a﹣b=____ 

芝麻、花生等硬果类食物中，含量较多的营养物质是（    ）

下列有关细胞中“一定”的说法，正确的是（  ）

①光合作用一定在叶绿体中进行 ②有氧呼吸一定在线粒体中进行，有H₂O生成的呼吸过程一定不是无氧呼吸，产生CO₂的呼吸过程一定不是无氧呼吸产生乳酸的过程 ③没有细胞结构的生物一定是原核生物 ④以RNA为遗传物质的生物一定是原核生物 ⑤所有生物的蛋白质一定是在核糖体上合成的 ⑥有中心体的生物一定不是高等植物．

图表示某种树叶的外形图，图中 、 、 、 分别代表不同的物质，箭头表示物质进出的方向，请据图回答下列问题：