Select the option that represents the letters that when sequentially placed in the blanks below will complete the letter series.
S _ P _ _ G _ I S G _ I _ _ P I

Let's analyze the given letter series: S _ P _ _ G _ I S G _ I _ _ P I
The total number of letters including spaces is 16. Let's try dividing it into 4 groups of 4 letters each:

S _ P _

_ G _ I

S G _ I

_ _ P I

By comparing group 3 (S G _ I) with group 2 (_ G _ I) and group 4 (_ _ P I):

We can deduce the repeating pattern is S G P I.

Let's complete each group using this pattern:

Group 1: S _ P _ → fill with G and I → S G P I

Group 2: _ G _ I → fill with S and P → S G P I

Group 3: S G _ I → fill with P → S G P I

Group 4: _ _ P I → fill with S and G → S G P I

The letters sequentially filled in the blanks are: G, I, S, P, P, S, G.
This matches option A.