In fact, I'd argue travel is an essential industry, an essential activity.

事实上，我甚至敢说旅行是必要产业、必要活动。

The tariff actions taken by the president are necessary to revive America's essential steel and aluminum industries.

特朗普总统的关税举措很有必要，可以复苏美国重要的钢铁产业和铝制品产业。

This timely book shows how economic, geopolitical and technological forces shaped an essential industry.

这本及时的书展示了经济、地缘政治和技术力量如何塑造一个重要行业。

The shallow lagoon surrounding the island of Mozia is ideal for extracting salt from the sea, and for thousands of years, locals have labored in salt pools like these as part of this essential industry.

莫齐亚岛周围的浅泻湖是从海中提取盐分的理想场所，数千年来，当地人一直在这样的盐池中劳作，作为这一重要行业的一部分。