甲、乙、丙、丁分别是Al₂(SO₄)₃、FeSO₄、NaOH、BaCl₂四种物质中的一种，若将丁溶液滴入乙溶液中，发现有白色沉淀生成，继续滴加沉淀消失；若将丁溶液滴入甲溶液中，无明显现象。据此可推断丙是

已知点P（﹣2， $\frac{\sqrt{14}}{2}$ ）在椭圆C： $\frac{x^2}{a^2}+\frac{y^2}{b^2}$ =1（a＞b＞0）上，过点P作圆C：x²+y²=2的切线，切点为A，B，若直线AB恰好过椭圆C的左焦点F，则a²+b²的值是（   ）

2016年3月，由谷歌公司研造的人工智能系统阿尔法围棋(AlphaGo)挑战围棋世界冠军李世石，最终以4比1获胜。阿尔法围棋拥有两个大脑—一落子选择器和棋局评估器，后者很像人脑在下围棋时凭直觉快速锁定策略的思维。由此可见（    ）

吉他上的弦绷紧时发声的音调比它不紧时高，则绷紧的弦发声比它不紧时（    ）

短文改错。
短文中共有10处语言错误，每行中最多两处错误。错误涉及一个单词的增加、删除或修改。
增加：在此处加一个漏字符号(∧)，并在其下面写出增加的词;
删除：把多余的词用斜线(＼)划掉;
修改：在错的词下划一横线，并在其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(从十一处起)不计分。
    I am angry about the behavior of dishonest in exams. This doesn't mean I've never cheated. I once write the answers on my hand for a history test, but unluckily caught by my teacher. Because she was one of my most favorites, there were no words to describe what sorry I felt at that time. I thought cheat would help me keep my straight A. Little I know that I was hurting not only me but also my teacher. From this lesson I know our teachers want their students to succeed by learning with their own and do the best they can, not by cheating.