Correct Answer: DCED

Solution : Given:
CD_E_DD_CD_E

To fill in the blanks, divide the series into clusters of 4 letters – CD_E / _DD_ / CD_E
Let's check each option –
First option: CDCD; CD C E / D DD C / CC D E (No repeated pattern found.)
Second option: DCCC; CD D E / C DD C / CC C E (No repeated pattern found.)
Third option: DCED; CD D E / C DD E / CD D E (CDDE is repeated in the series.)
Fourth option: DDDC; CD D E / D DD D / CD C E (No repeated pattern found.)

So, the series becomes→CDDECDDECDDE. Hence, the third option is correct.