Language tasks a child can do only with an able adult's help lie in:

1. Vygotsky's zone of proximal development covers tasks a child can do with guidance but not alone. 2. Applied to language, it covers linguistic tasks such as syntax or vocabulary use that the child can do when helped. 3. The critical period, silent listening and jargon babble are not about adult-assisted tasks. 4. So the answer is the zone of proximal development. **Why not the others:** The critical period concerns age limits, silent listening concerns waiting before speaking, and jargon is a babbling stage. _Source: Wikipedia, "Language acquisition", section "Social interactionism" (revision 1375526787)_