"If you go to the movie theater, take your sister."
Translation:Si vas al cine, lleva a tu hermana.
Hola Tristan.Cozens: It is not subjunctive because the action is an "open condition"; that is, it is highly likely that the brother WILL go to the movies, The mother (the speaker) has no doubt that he will be going. Therefore, there is no trigger for subjunctive; that is, no doubt or mystery. Also, it is a rule that in the present tense, we never use subjunctive after "si". Here is a link if you would like to study more: http://spanish.about.com/od/verbs/qt/si_clause.htm CHAU
The reflexive in Spanish is a lot more common than it is in English, and some verbs actually need it to work. Other verbs change their meaning if they are used in the reflexive ("ir" means "to go" whereas "irse" means "to leave"). In this case, the meaning stays almost the same (thus, both "lleva" and "llévate" are accepted as correct). But "llévate" would mean something like "take your sister with you". In Spanish, it sounds a lot more natural to use the reflexive here.
Oh, I forgot to mention, check out this Slideshare presentation for a good summary of the reflexive: http://www.slideshare.net/tavobalcazar/gramtica-1-verbos-reflexivos
There does not seem to be any acceptable 'usted' translations for this sentence.
I don't understand the two "correct" solutions. One is "Si vas al cine, llévate a tu hermana, and the second is "Si va al cine, lleva a su hermana. What makes the sentence use a reflexive verb with the tú form?
Hola Amigos: "Llévate" is a way to combine the imperative "take" (lleva) with the personal pronoun "tú". "Lleva" means (command) TAKE! It implies "you take!". "Llévate" emphasizes the "you" = "YOU take!"