湖底沉积了大量的泥沙。

hú dǐ chénjī le dàliàng de ní shā.

A large amount of silt has accumulated at the bottom of the lake.

把箱子翻过来，看看底上写了什么。

bǎ xiāngzi fān guòlái, kànkan dǐ shàng xiě le shénme.

Turn the box over and see what's written on the bottom.

鞋底已经磨得很薄了，该换双新鞋了。

xié dǐ yǐjīng mó de hěn báo le, gāi huàn shuāng xīn xié le.

The soles of the shoes have been worn very thin; it's time for a new pair.