In a sequence of letters: A, C, E, G, ?, K. What is the missing letter?

C. H

In the sequence A, B, C, ?, E, F, what character should replace the question mark?

A. D

In the sequence A, B, C, D, ?, F, G, what character should replace the question mark?

A. E

In the sequence A, B, C, ?, E, F, what character should replace the question mark?

A. D

In the sequence A, B, C, ?, E, F, what character should replace the question mark?

A. D