实验室制取二氧化碳和氢气都用到的一种物质是（　　）

已知两个非零向量$\overrightarrow{a}$与$\overrightarrow{b}$，定义$|\overrightarrow{a}\times \overrightarrow{b}|=\left|\overrightarrow{a}\right|\left|\overrightarrow{b}\right|\sin \theta$，其中$\theta$为$\overrightarrow{a}$与$\overrightarrow{b}$的夹角，若$\overrightarrow{a}$=(-3,4),$\overrightarrow{b}$=(0,2)，则$|\overrightarrow{a}\times \overrightarrow{b}|$的值为(  )

鲜豆浆含有丰富的优质蛋白质及多种人体所需的微量元素，素有“绿色牛乳”之称．豆浆中的营养物质主要来自于黄豆的（　　）

    Tanzania（坦桑尼亚）is a country which has a lot of animals, such as gnus（角马）, lions, cheetahs（猎豹, elephants, giraffes, crocodiles and so on. Every year, many people in the world travel to this African country to watch the animals closely. But do you know how they travel?

    By bus—This is the most common way. When people get on a bus, they'll find that the bus is a little strange. It is different from the buses we often see. There are no big windows at all, but some small windows. And it looks like a cage. What are they used for? Oh, people can use it to watch animals, especially those dangerous animals, and take photos. We know that people are most interested in the lions. So when two buses meet, the drivers will stop and ask each other whether they have found lions.

    By boat—We can often see many people are in a boat, enjoying the beautiful scene along a river of a lake, and they can also enjoy hippos（河马）and crocodiles from a nearer distance.

    By hot balloon（热气球）—In the early morning, when the sun is beginning to rise, a large hot balloon is also starting its journey. Taking a hot balloon makes most of the travelers excited. After some time, the balloon will land in a certain place, and the waiters will serve people a delicious and special breakfast. But the cost of taking a hot balloon is also very high. A person should pay 400 dollars for an hour's trip.