extremely

The desert air becomes extremely cold once the sun sets below the horizon.

(Chinese) 太阳落山后，沙漠里的空气会变得极其寒冷。

It is extremely difficult to climb Mount Everest without the help of oxygen tanks.

(Chinese) 在没有氧气瓶帮助的情况下攀登珠穆朗玛峰是极其困难的。