Which of the letters will come next in the following series?
$a, ab, abc, abcd, abcde, abcde, ?$

The positions of how many digits in the number $7,3,5,4,6,1,2$ will remain unchanged after the digits within the number are rearranged in descending order from left to right?

To answer these questions study carefully the following arrangement of letters, digits and symbols.

$6,=,\$, C,E, 3,8 ,G,L,M, 7, \star, @ ,P,R, 4, \# ,N,T, 5, S,V$

If all the symbols in the arrangement are removed, then which of the following will be the $7^{th}$ to the left of the $13^{th}$ element from the left end?

Study the following arrangement carefully and answer the question.
$O, 4, E, J, 5, T, 1, A, M, Q, 3, 8, N, I, K, 7, W, F, 6, S, 9, U, 2, Y, X$
If all the numbers in the above arrangement are dropped,which of the following will be the ninth to the left of $S$?

The positions of how many digits in the number $53147926$ will remain unchanged after the digits within the number are rearranged in descending order?

Choose the correct alternative to complete the series: $ab . . aa . . bbb . . . aaa . . bbaa$