Why, According to Kant, Does Failing to Help Those in Need

Why, according to Kant, does failing to help those in need amount to failing to treat humanity as an end in itself?

A) Because treating humanity as an end in itself requires trying, whenever possible, to promote others' goals and interests, not just your own.
B) Because treating humanity as end in itself amounts to treating all humans as you would want to be treated, which includes helping others when they need help.
C) Because treating humanity as an end in itself means imposing a limit on your selfish inclinations.
D) Because treating humanity as an end in itself means promoting not only your own talents but also those of others, which means ensuring that they have what they need to develop their own talents.