Explanation:

Let's break down the order using a dictionary approach:

- Signed: Comes first as it ends with "-ed", making it alphabetically first among these five words.

- Significant: Follows after "Signed" as the next in the alphabetical order.

- Simplify: Comes next since "Simp" is after "Signi".

- Sinful: Comes after "Simplify" since "Sin" is alphabetically after "Simp".

- Singing: "Singing" comes last as "-ging" is after "-ful" in "Sinful."

Now, let's review the options:

- 1, 3, 1, 5, 2, 4

- 2, 3, 5, 1, 2, 4

- 3, 3, 2, 1, 5, 4

- 4, 3, 1, 2, 5, 4

The correct sequence: 3, 1, 5, 2, 4