已知x=3y=1是关于x，y的方程组mx+ny=7nx-my=-1的解，求2m+

阅读理解。

     At the age of sixty-seven, Shirley Yeats decided to take a trip.Everything was fine until one day the smoke

was coming out of another room on the ship. She phoned the captain (船长) from her room at once and told

him about the fire. Then she went out to see what she could do to help. Later on, she found that the fire

spread (蔓延) very quickly. The captain decided to get all the passengers (乘客) out as quickly as

possible when he saw that.       

     Many of the other passengers were very afraid of that, but Shirley didn't seem scared at all. To many

people's surprise, she didn't go to the lifeboats but help the other passengers instead.

     At last, all one thousand passengers were in the lifeboats and nobody died in the fire. Shirley was one of

the last people to leave. Later she told others, "I was very scared, but I always knew what I had to do. I think

all my years as a teacher helped—all the time telling people what to do and how to do it."

1. The story mainly about _____. [ ]

A. A girl called Shirley Yeats.

B. A fire on the sea.

C. What an old woman teacher did when a fire happened.

2. When Shirley Yeats found the fire, what did she do first?  [ ]

A. She slept in her room.

B. She called the captain and told him about the fire.

C. She went into the lifeboat quickly.

3. Which of the following is TRUE? [ ]

A. Shirley Yeats wasn't scared at all.

B. Shirley was sixty-six.

C. Nobody died in the fire.

4. The underlined word "scared" means _____.[ ]

A. 害怕的

B. 惊奇的

C. 愉快的

5. What do you think of a teacher from the story? [ ]

A. It's a very usual job.

B. A teacher is telling people what to do and how to do it all the time.

C. It's a dangerous job.

课外教育的特点是组织上的自愿性、（）、活动的自由性、形式的多样性。

提升钢丝绳的捻向，分为右捻和左捻两种。

¹⁵N的培养基上生长的大肠杆菌，其DNA分子均为¹⁴N—DNA（对照）；在氮源为¹⁵N的培养基上生长的大肠杆菌，其DNA分子均为¹⁵N—DNA（亲代）。将亲代大肠杆菌转移到含¹⁴N的培养基上，再连续繁殖两代（Ⅰ和Ⅱ），用某种离心方法分离得到的结果如图所示：

将第一代（Ⅰ）细菌转移到含¹⁵N的培养基上繁殖一代，将所得到细菌的DNA用同样方法分离，请参照甲图，将DNA分子可能出现在试管中的位置在乙图中标出。