Final answer:
The sentence should be completed with 'concentrate' to indicate that Abe, being older, has the ability to focus for longer periods than his younger brother Alex.
Step-by-step explanation:
Abe is in school; he is able to concentrate longer than his younger brother Alex can. This sentence is meant to be completed with a verb that shows an ability that Abe has, which is greater than that of his younger brother. In the context of cognitive or academic abilities, which typically develop as children grow older, the word concentrate fits well. This is particularly relevant in an educational setting, where older students like Abe often have longer attention spans and are better able to focus on tasks compared to younger students like Alex. The capacity to concentrate and focus is crucial for tasks such as completing homework, studying for exams or even participating in class discussions. As children mature, their cognitive abilities develop, enabling them to handle more complex tasks and engage in activities that require sustained attention for longer periods.