What is the plural form of el pupitre?

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?

Fill in the blank with the spanish word that best completes the sentence. las chicas son de méxico. ellas son mexica mexicanos mexicano mexicanas

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