把下面一组数按从大到小的顺序排列起来． $5.4\dot{5}$ ，5 $\frac{9}{20}$ ，5.5，5.454

Welcome to the Kids' Science Challenge!

    Do you like science projects and winning some awesome gifts? This is the challenge for you. What's even better is that you don't have to build anything--simply come up with an original idea or design that relates to one of three topics given below.

Wonderful Sounds

    Ready for Wonderful Sounds? Click on Science Secrets to meet our sound specialist. And be sure to download fun activities with crazy new sounds and musical instruments in the Dig In section! Now what kind of new musical instrument can you invent?

Super Material for Sports

    Ready for Super Material for Sports? You'll discover the amazing world of Materials Science, where scientists and engineers develop new materials for everyday functions--like sports! Click on Science Secrets for information about our scientist. And don't forget to download the fun activities in the Dig In section! Now can you come up with a new sports material that would help you play your favorite sport?

Magical Microbes

    Ready to discover Magical Microbes, the tiniest living things on earth? Click on Science Secrets for information about our scientists. And be sure to download all the fun activities in the Dig In section! Now can you think of a brand new way that microbes can help people?

点M与点F（4，0）的距离比它到直线l：x+5=0的距离小1，则点M的轨迹方程是____ 

现代通信技术的发展，拉近了人们的____，增进了人们之间的____，地球成为一个“小小的村落”。