文字稿:

After almost dying out in the 1970s, a kind of whistling language is now undergoing a revival.

Silbo Gomero, as it's known, has become a compulsory subject in one school in Spain's Canary Islands.

The whistling approximates the sounds of the Spanish language.

It can be heard from two miles away, and was used to communicate across valleys and ravines before the arrival of telephones.

Vocabulary 词汇:

dying out 正在消失的

undergoing a revival 趋于重振

compulsory 必需的，强迫的

approximates 模仿，接近于

ravines 峡谷