The “illustrates which one†question stem tells us that we are trying to take the situation described in the passage and turn it into an abstract proposition.
What was the situation in the passage? Children couldn’t remember their phone numbers, despite being familiar with digits. The children learned their phone numbers by using a song.
You mentioned that you were torn between A and E. E is correct because it takes that situation and translates it into an abstract proposition: songs are useful in helping children remember the order in which familiar words (in this case digits) occur.
Why is A incorrect? It gives us the proposition that there are some things that children CANNOT learn without the aid of songs. Notice that this is a much stronger statement: it is saying that the ONLY way (“cannot learn withoutâ€) children can learn certain things is with songs.
Did the passage tell us that? No — the passage simply said that in this case the children could not remember something, and that songs were one way to help them learn. Perhaps the children could have also learned if they were taught to visualize their phone number — nothing in the passage would be inconsistent with that possibility. But answer A would, and that is something that the passage just didn’t give us.
I hope that helps! Let us know if you have further questions.