Final answer:
Children in the two-word phase struggle with phrases like "the car bumped the truck" due to a lack of syntactic awareness, as they're still learning how to construct proper sentence structures.
Step-by-step explanation:
At the two-word phase, children have trouble with "the car bumped the truck" primarily due to B) Lack of syntactic awareness.
At this stage of development, children are rapidly expanding their vocabulary and starting to understand the specific rules of their language.
However, their ability to put words together in a syntactically correct manner is still developing. While they may understand individual words, constructing a phrase that involves a clear subject-verb-object structure -- as in "the car bumped the truck" -- requires a syntactic awareness that they are just beginning to develop.