Riddle #01 answer is ‘S’.
This series means the sequence of ‘week’.
Once upon a time, Dongyi people made the concept of a week, it is called ‘Chil-hoe-ryuk’ a calendar of 7 days circulation.
And sometimes there is a gathering of five stars between moon and sun at sunset time.
At that time, the sequence of five stars is Mars, Mercury, Jupiter, Venus and Saturn.
So, a week sequence is like as;
Monday: Moon
Tuesday: Mars
Wednesday: Mercury
Thursday: Jupiter
Friday: Venus
Saturday: Saturn
Sunday: Sun
Therefore the answer of riddle is ‘S’ of Saturn.