Sostenible, (Past Tense) - One-Year Digital Student Package (FlexText® + Explorer)ISBN: 978 1 641593 12 0 2021 One year subscription to Sostenible, Spanish (Past Tense) Student Edition FlextText and Explorer. Access code to subscription will be included in an email following your purchase. Students must be enrolled in a class to access the digital material. Teachers need to purchase the One Year Teacher Digital Package to create a class on the Learning Site and gain access to the digital material. (Teacher's guide, audio, and