为了形成封闭的冻结圈，先要在井筒周围钻一定数量的冻结孔，冻结_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题单项选择题

为了形成封闭的冻结圈，先要在井筒周围钻一定数量的冻结孔，冻结孔一般等距离地布置在与井筒同心的圆周上。冻结孔间距一般为（）。

A.1.2～1.5m

B.1.2～1.8m

C.1.2～2.0m

D.1.5～2.0m

答案

参考答案：A

完形填空

完形填空。

Dear Sigmund Friend
     I am a Grade 9 student. I have  1 problem, and I do not know how to deal  2  it.
    I have a lot of homework every day, and I have no choice  3  to do it. I often stay up late to complete  4 ,
and then feel tired the next day.
     Sometimes, I want to  5 to do so much work, but usually I just accept it. I understand that it is important
to do my homework and  6  on time. However, I hardly have any spare time for my hobbies  7 playing
volleyball and ping-pong. I really feel bad about that. I often doubt whether it is worth  8 so hard.
    I am  9 a holiday without homework so that I can relax and have some time for my hobbies. What should I
do? Can you offer me some suggestions? They will be of great value to me. I hope to  10 you soon.
                                                                                                                                   Best wishes
                                                                                                                                        Millie

( )1. A. an
( )2. A. with
( )3. A. and
( )4. A. the housework
( )5. A. accept
( )6. A. hand it on
( )7. A. as
( )8. A. reading
( )9. A. looking for
( )10. A. hear of

B. a
B. for
B. so
B. the exercise
B. refuse
B. hand it in
B. such so
B. playing
B. looking forward to
B. hear about

C. the
C. to
C. but
C. exercises
C. take
C. hand in
C. such as
C. walking
C. looking after
C. hear from

D. (不填)
D. on
D. then
D. the exercises
D. agree
D. put it in
D. as much as
D. working
D. looking up
D. hear

选择题

已知数列{a_n}（n∈N^*）的前n项和Sn=-n2+1，则a₆=（　　）

A．11

B．-11

C．13

D．-13