能区分咯血和呕血的主要依据是　　　　　　　　　　　　　　　　_爱下问搜题

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问题单项选择题

能区分咯血和呕血的主要依据是　　　　　　　　　　　　　　　　　

A．是否从口而出

B．血液酸性或碱性

C．出血量的大小

D．有无黑便

E．有否贫血

答案

参考答案：B

阅读理解

阅读并排序。下面的短文由六个段落组成，开头和结尾已给出，其余的四个段落均是随机排列的。请根
据段落之间的逻辑关系，重新排列这四个段落的顺序，使短文通顺。

Samuel Clemens was born in 1835, Missouri. When he was four, his family moved to the town of
Hannibal, a port on the Mississippi River, and Clemens loved to watch the big steamboats going up and
down the river. He said that all the boys in his school had one ambition in life: to work on a steamboat.

     A. In 1857, he achieved his ambition and got a job working on a steamboat. He sailed up and down the wide
Mississippi River until the American Civil War began.
     B. His father died when he was just 12 years old and Clemens then went to work for a printer to help support
his family. He traveled around, and worked in many different cities.
     C. In 1865, Clemens wrote a story about a jumping frog with his pen-name. The story and the writer became
famous. After that, he wrote many books, including The Adventures of Tom Sawyer. It was published in 1876.
He also gave many lectures, and became a very famous and popular man.
     D. Clemens moved around the USA on the steamboat, and tried several jobs. He was a soldier, and a silver
miner. And then he started working as a writer for a newspaper. At this time, he decided to use a pen-name for
his stories, and he chose the name "Mark Twain". Samuel Clemens died in 1910. He is considered to be one of
the greatest writers in American history.
     正确的顺序：

判断题

RNA分子可以发生热变性，并有增色效应