超高压长线路末端空载变压器的操作应注意什么？

阅读理解。

     Tom is the son of a farm owner. One New Year's Day, when he was 15, his father asked him to

work on the farm for one year when he was free. Tom was unhappy with his father's idea. "That isn't my

job,  I have too much schoolwork to do." Hearing this, his father said,"I promise (许诺) to give you the

best present if you can finish one year's work." Tom thought for a while and agreed.

     Starting one Saturday, the boy got up early and worked hard until evening, just like any other farmer.  

Time passed quickly. Tom's crops (庄稼) grew well. On the last day of the year, the father called his son

to him, "I'm happy to see that you have worked very hard in the whole year," said the father, "Now, tell

me what you want. "

     The boy smiled and showed his father a big piece of bread made from his wheat. "I've already got the

best present. No pains, no gains. I think this is what you wanted me to know." His father was quite

pleased to hear that.

1. Where did Tom's father work?

2. What did Tom's father want him to do when he was 15?

3. How did Tom work on the farm in the whole year?

4. Did Tom get the best present at last?

5. What do you think of Tom's father?

关于叶酸，下列哪项是对的（）。

A.耐热

B.在酸性环境中稳定

C.存在于绿叶蔬菜，水果和动物内脏等食品中

D.每天需要约100mg

E.人体叶酸主要贮存于脾脏

流行病学研究方法的核心特征是（）

A.群体特征

B.以分布为起点的特征

C.对比的特征

D.概率论与数理统计的特征

E.社会医学和预防为主的特征

以太网是( )。

A．总线网

B．FDDI

C．令牌环网

D．星形网

井下机电设备硐室应当设在进风风流中；该硐室采用扩散通风的，其深度不得超过（）m，入口宽度不得小于1.5m，并且无瓦斯涌出。井下个别机电设备设在回风流中的，必须安装甲烷传感器并具备甲烷超限断电功能。

A、3

B、4

C、6