Una persona que 'nada bien' es una persona que tiene la habilidad y destreza para nadar en el agua.
A person who 'nada bien' is a person who has the ability and skill to swim in the water.
You use preterite to describe an action that took place and was fully done, Ex. José entro a la habitación, you can see John went into the room, he completed the action. On the other hand, imperfect tense doesn't specificate if the action was completed, Ex. José entraba a la habitación, it doesn't tell us if José fully entered the room.
<span>Él es un compañero de clase is the right answer. The 1st sentence is ella but </span>compañero should be compañera. In the second one ella should not have an accent mark and in the last one el doesn't match with una.
The level of quality and complexity of flamenco is comparable to that of jazz and classical music.