Dear Betty,

    I'm your eraser Jill. This afternoon you lost me in your classroom. Simon found me and gave me to your English teacher Ms. Green. Now Ms. Green's three keys and I are in Ms. Green's bag. The bag is yellow. It's on Ms. Green's desk. Please call Ms. Green at 718-0167 and ask her for me. You can come to the library, too. Ms. Green is in the library now.

Jill

把耳朵贴在铁轨上，就可以断定是否有火车要到来，这说明火车的声音可以通过____传送过来的。

对于生长在农田中的青蛙来说，它的环境是指（　　）

如图中甲、乙、丙、丁四根弹簧完全相同，甲、乙左端固定在墙上，图中所示的力F均为水平方向，大小相等，丙、丁所受的力均在一条直线上，四根弹簧在力的作用下均处于静止状态，其长度分别是L_甲、L_乙、L_丙、L_丁，下列选项正确的是（   ）