Choose the correct alternative to complete the series: $ba....b...aab....a...b$

What will be the next term in the series: $BDF, CFI, DHL, ?$

Choose the correct alternative to complete the series: $....op....mo.....n....\,...pnmop.....$

Choose the correct alternative to fill in the blanks in the series: $c . . b b a . . . . c a b . . . . a c . . . . a b . . . . a c$

Study the following arrangement carefully and answer the question given below:
$R, 4, E, J, 5, T, 1, A, M, Q, 3, 8, N, I, K, 7, W, F, 6, D, 9, U, 2, Y, V$
How many such numbers are there in the above arrangement,each of which is immediately preceded by a consonant but not immediately followed by a consonant?

Fill in the blank space for the given series with the correct alternative.
$1, 2, 5, 12, 27, 58, 121, (\ldots)$