What character should replace the question mark in the sequence 3, 6, 9, ?, 15?

A. 12

In the sequence P, Q, R, ?, T, U, what character is missing?

A. S

Identify the missing letter in the pattern: X, Y, ?, A, B.

A. Z

In the sequence: A1, B2, C3, ?, E5, what should replace the question mark?

A. D4

Identify the missing character in the series 1, 4, 9, ?, 25.

A. 16