北方以水运为主。(   )

据BBC报道，前英国政府辐射事务顾问巴斯比博士表示，日本核电站的问题极为严重，尤其令人担心的是福岛核电站三号反应堆。他称，该反应堆现在遇到了麻烦，因为它使用的是一种不同的燃料：它不是铀，而是一种铀钚混合燃料，而钚是极为危险的，因此一旦这种物质泄漏出来，将使海啸灾难雪上加霜。钚是世界上毒性第二大的物质（世界上毒性第一大的物质为钋）。一片药片大小的钚，足以毒死2亿人，5克的钚足以毒死所有人类。钚的毒性比砒霜大4．86亿奥倍，一旦泄露入太平洋全人类都玩完！239Pu，半衰期24390年。关于钚的危害的认识，你认为错误的是（  ）

能一次区分CH₃COOH、CH₃CH₂OH、C₆H₆、C₆H₅NO₂四种物质的试剂是

完形填空

    People all over the world eat rice. 1 people in Asia (亚洲), Africa (非洲) and South America 2 it every day of their lives. Some people almost don't eat 3 except rice.

    Rice is a kind of 4. There are more than 7, 000 kinds of rice. Most kinds are water plants. Farmers 5rice in many countries even in the southern part of Russia and in eastern Australia.

    No one really knows where rice 6. Someone in China wrote about it almost 5,000 years ago. Some scientists (科学家) think that rice 7 in West Africa first, but 8 think it 9from India and then was 10to other parts of the world.

在一定温度下将各1mol CO和水蒸气放在密闭的容器中反应：CO（g）+H₂O（g） CO₂（g）+ H₂（g）达到平衡后，测得CO₂为0．6mol，再通入4mol水蒸气，达到平衡后CO₂的物质的量为