How do you say “i know elena” in spanish

Okay so i'm taking an online spanish course (penn foster), and in the study guide, you have to create a bunch of sentences with words you've learned so far. translating, reading, and those kinds of things are fairly easy, but when it comes to making my own sentences, my brain just kinda waltz's away. anyone got any tips?

Choose the best spanish equivalent to the phrase. mauricio sang that song. mauricio cantó esa canción. mauricio canté esa canción. mauricio cantaron esa canción. mauricio cantamos esa canción.

Which of the following sentences needs the personal a in the bank?