The example is 1 x (9 x 5) = 45
Using the associative property of multiplication, we basically rearrange the parenthesis to group the first two terms like so: (1 x 9) x 5
So this is why choice D (1 x 9) x 5 = 45 is the answer
This means that 1 x (9x 5) = (1 x 9) x 5 is a true equation