Select the option that represents the letters that, when sequentially placed from left to right in the following blanks, will complete the letter-series.
A _ _ U S _ P R _ S A P _ U _ A _ R U _

Let's count the total number of elements including blanks. The pattern has 20 positions. Let's try dividing it into groups of 5 letters:
A _ _ U S | _ P R _ S | A P _ U _ | A _ R U _

Let's look at the repeating structure. Notice the presence of letters like A, P, R, U, S.
It looks like the repeating pattern block is APRUS.

Let's check if APRUS fits perfectly across all 4 groups:

A P R U S (Blanks: P, R)

A P R U S (Blanks: A, U)

A P R U S (Blanks: R, S)

A P R U S (Blanks: P, S)

Let's collect the filled blanks in sequence:
P, R, A, U, R, S, P, S

This matches option D: PRAURSPS.