9 see joke: The person was swarmed in opern, there are a lot of geminate and didymous lovers in the audience.

歌剧院中挤满了人，观众中有许多成双成对的情人。

The key reason for the improved performance are the pairs of counterrotating swirls created at either side of the leading-edge bumps, called tubercles.

隆前缘能增进性能的关键理由，是因为在这些隆节瘤的两侧，会产生成对的反向旋转涡流。