The missing character is J.
The sequence is a list of letters that are two places apart in the alphabet, starting with A. The next letter in the sequence is J, which is two places after B.
A. G is not the missing character because it is not two places after B. B. J is the missing character because it is two places after B. C. P is not the missing character because it is not two places after B. D. U is not the missing character because it is not two places after B.
