Fill in the blank space for the given series with the correct alternative.
$3, 7, 15, 31, 63, (\dots)$

Which of the following will come in place of the question mark $(?)$ in the order given below?
$AE, CG, EI, GK, ?$

Fill in the blank space for the given series with the correct alternative.
$6, 15, (\ldots), 45, 66, 91$

In the set of three-digit numbers given below,the first two digits of each number are interchanged. Which one among them will be in the middle if they are arranged in ascending order after the change?
$230, 422, 328, 516, 138$

Choose the alternative that will complete the series:
$aku, fpz, kue, (\ldots), ueo, zjt$

Choose the correct alternative to fill in the blanks in the series: $ab...bcbca...c...bab$