Study the letter series given below and answer the question that follows:
$H, D, Y, S, M, W, N, B, Q, P, O, C, R, T, B, L, Z, V, E, G, U, F$
Which is the only letter that occurs twice?

$A$ group of letters is given which are numbered $1, 2, 3, 4, 5$ and $6$. Below are given four alternatives containing combinations of these numbers. Select the combination of numbers so that the letters arranged accordingly form a meaningful word.
$A, E, H, R, K, N$
$1, 2, 3, 4, 5, 6$

Which of the following series observes the rule,"Skip in between adjacent letters,increasing one letter more each time to build a set of letters"?

In the following list of letters,how many $O$'s are followed by $Q$'s but not preceded by $D$'s?
$D, O, Q, O, D, Q, O, D, O, D, Q, D, O, Q, D, S, D, Q, P$
$O, Q, D, S, S, S, D, O, Q, O, Q, D, O, Q, D, D, O, Q$

Arrange the given words in alphabetical order and choose the one that comes first.

Arrange the given words in alphabetical order and choose the one that comes first.