Fill in the blank space for the given series with the correct alternative.
$34, 18, 10, 6, 4, (...)$

How many such numbers are there in the following series,each of which is immediately preceded by $6$ but not immediately followed by $4$?
$3, 8, 6, 8, 4, 2, 6, 9, 8, 4, 6, 8, 4, 8, 6, 2, 6, 8, 4, 8$

What would come next in the following number sequence?
$2, 3, 2, 3, 4, 2, 3, 4, 5, 2, 3, 4, 5, 6, 2, 3, 4, 5, 6, 7, 2, 3, 4$

Find out the missing term for the given series from the given alternatives:
$HS, JQ, LO, NM, (?)$

Choose the correct alternative to complete the series: $m, n, o, p, q, o, p, q, r, s, \dots$

Choose the correct alternative to complete the series: $...bbca...bcca...ac...a...cb$