Our airline offers three classes of seats: economy, business, and first.

我們航空公司提供三種艙等:經濟艙、商務艙和頭等艙。

This product falls into a different class of goods, so the import tax is higher.

這項產品屬於另一類貨品,所以進口稅比較高。

Please ship the documents by first-class mail so they arrive before Friday's meeting.

請用第一類郵件寄送這些文件,讓它們在週五會議前送達。