B. The first verb in a pivotal construction does not take verb-suffix le了. The second verb takes a sentence-end le了if the action is completed. If the object of the second verb is quantified or modified, the second verb takes the verb-suffix le了.

 

          Zuótiān tā qǐng(x) wǒ chī-le yí dùn Zhōngguó fàn. 

          昨天他请我吃了一顿中国饭。

Yesterday he invited me to eat a meal of Chinese food.