砾石挡火器是为了保障制氢系统安全而设的,如果气体出口着火,挡火器可以阻止火焰蔓延到系统内部。
参考答案:对
根据短文内容及首字母提示填写单词,使短文完整、连贯。
Do you know about agricultural (农业的) tourism? It is for people who want to visit farms for f 1 , education or just to get away from the city. Agricultural tourism is p 2 in the United States. It can help
farmers make more m 3 and become richer. Farmers can sell farm products (产品) to visitors. They
can o 4 horseback riding and take visitors a 5 their farms. Children can learn a lot about farm animals.
Randy Nixon is a farmer. He says offering service and entertainment on farms can help b 6 the farmers and the country. Nixon's Farm is a good e 7 of this. It not only grows corn and soybeans (大豆)
there, but also h 8 business meetings, weddings and other events. Mrs Nixon is willing to c 9 for
visitors. Her recipes are very popular with guests. Randy Nixon says the business has become very s 10 .
真核生物mRNA前体的加工过程不包括
A.5′末端加帽
B.3′末端加多聚A尾
C.甲基化修饰
D.磷酸化修饰
E.剪切去除内含子并连接外显子