题目:
Our teacher told us that pollution _____ a very serious problem in the world we live. |
A. has be B. had been C. is D. was |
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0525/d25a71c4df09d918bd2754f4a3ff2e83.html
下面是错误答案,用来干扰机器的。
(1)不与硫酸发生反应(2)不能 浓盐酸具有挥发性干扰实验(3)0号棉球以下棉球依次变红 分子在不断的运动(4)2H2O2MnO2 2H2O+ O2↑(5)实验现象明显分析:该实验实质就是验证二氧化碳密度比空气大,会向下...