I am not a teacher.
There are several issues here, including that of gender neutrality.
'Himself', apart from when referring to a male, used to be the default, all purpose, general term used when the gender of the person was unknown or irrelevant. For many people this is no longer acceptable, and the choice is then either, 'himself or herself' or using a plural genderless pronoun. This, of course, causes problems of agreement which are either ignored, or avoided by turning the subject into a plural too. e.g. 'There isn't enough love capable of filling the emptiness of people who don't love themselves.'
As for your sentences, I would probably use a) because I haven't lived in an English speaking country since this became a problem, so anything else seems unnatural.
I would not say b).
c) is wrong.
I don't like d).