[WriterGirl_15]

Okay, so I've been having trouble with my high school spanish one class, especially when to leave a pronoun subject understood and when to write it out. I went back and redid an assignment with that, and after reading this page:
http://spanish.about.com/od/pronouns/a/subject_pronoun.htm
I think I understand. But there's one that, from what I understand, should be left understood. However, the answer key says it has to be written in. The assignment was to change simple progressive verbs to present progressive. The problem was "Vosotros hablais con vuestro jefe." My answer was "Estais hablando con vuestro jefe." The answer key used my answer, but it started with the subject (vosotros). What I need to know is why. Please help me!