Which sentence structure is likely to challenge younger students' comprehension?

The sentence "Unless everyone has arrived, they cannot leave" is more complex due to its conditional structure, which introduces a subordinate clause. This type of structure requires students to understand not only the main idea but also the relationship between the condition and the outcome. The use of 'unless' creates a dependent clause that can challenge younger students who may still be mastering the concept of conditional reasoning or the function of conjunctions.

Students may struggle with identifying the core meaning of the sentence because they need to mentally process the requirement (or lack thereof) of everyone arriving before they can understand the action of leaving. Simpler sentence structures, like those in the other choices, typically present a single idea and are more straightforward, making them easier for younger learners to grasp.