孩子们不喜欢吃面包边，总是把硬皮剩在盘子里。

The kids don't like to eat bread ___crusts and always leave them on the plate.

雪地上形成了一层坚硬的冰壳。

A hard ___crust formed on the surface of the snow overnight.

地球的外壳主要由岩石构成。

The Earth's ___crust is mainly composed of rocks.