把下面排列错乱的句子，调整成连贯通顺的一段话，在横线上写上序号。

____用这个时间乘30万公里，除以2，就得出地球与月球之间的距离。

____人们利用激光制作的测距仪，可以测量地球到月球的距离。

____这样测算出来的距离是很精确的。

____激光是最准的尺。

____光的速度是每秒30万公里。从地球上射向月球的激光，两秒多钟就可以往返一趟。

____激光测距仪产生一束光，照射到月球上，又从月球反射回来。

Ladies and Gentlemen，

    Thank you for coming to attend the graduate ceremony.First of all，I'd like to 1 all the students who are here today.I remember  2 all of you when you were just starting Grade 7 at this school.You were so full of energy and thirsty 3 knowledge.And some of you were a little difficult to deal with！But today，you've all grown up so 4 and I am so proud of you.

    Although you've all worked very hard over the last three years，none of you did it 5 .I hope you'll remember the important 6 in your lives who helped and supported you.Please consider what they've done for you.Never 7 to be thankful to the people around you.

    Lastly，the end of junior high school is the beginning of a new  8 .You will have many difficult tasks 9 you.You'll make mistakes along the way，but the key is to 10 your mistakes and never give up.But along with difficulties，there will also be many  11 things waiting for you.Learn the new things，and you'll have the ability to make your own choices.Choose  12 and be responsible for your decisions and actions.  13 you have to go your separate ways now，I hope that you'll come back to visit our school in a few years' time.As you 14 on your new journey，you shouldn't forget where you came form.The future is 15 .

    Good luck and hope to see you again sometime soon！