For Alison's approach:

What happens to the numbers as you go down the rows?
What happens as you go up the rows?

For Bernard's approach:

Which numbers end in a 0 in row $A_2$?
Which numbers end in a 0 in row $A_3$?
Which of these sequences will hit 1000?

For Charlie's approach:

Can you find a similar method to Charlie's to describe the other rows?
Which descriptions include 1000?