看图完成句子 一空一词。

1. How many boys and girls are there in the picture?

    There are _____ boys and _____ girls.

2. What's the weather like in the picture?

    It's _____ and _____.

3. What are the girls wearing? 

    They're wearing _____ and _____.

4. What's the boy in sweater doing? 

    He's playing the _____ and _____.

5. What are the other people doing?

    They're _____ to the boy _____ singing songs.

如图1所示。一对平行光滑轨道放置在水面上，两轨道间距l=0.20m，电阻R=1.0 Ω；有一导体杆静止地放在轨道上，与两轨道垂直，杆及轨道的电阻皆可忽略不计，整个装置处于磁感强度B=0.50T的匀强磁场中，磁场方向垂直轨道面向下。现有一外力F沿轨道方向拉杆，使之做匀加速运动，测得力F与相同t的关系如图2所示。求杆的质量m和加速度a。