I had this same thought when I come across difficult people. Sometimes I think to myself, if there is no such difficult people, I cannot practice compassion with. If there is nobody in trouble, no one who requires help, I would not be able to collect merits. I don't hold any bodhicitta vows but with this in mind, I understood your question as a matter of interdependency. So the answer is A and B. a. The holders of the bodhicitta vows and sentient beings are dependent on each other to achieve and realise the cessation of sufferings.
In Yonten Shigyurma, The Foundation of All Realisations, it says:-
With mindfulness, introspection, and great care ?induced by that pure aspiration?, bless me to make my essential practice ?the Pratimoksha, root of Buddha’s teachings.
Just as I’ve fallen in this sea of suffering? so have all beings, my kind mothers;? seeing this, bless me to train in Bodhicitta, ?taking up the burden of liberating them.
And yet, just wishing this, without practicing ?the three ethics, Enlightenment cannot be attained.? Knowing this well, please bless me to intensively ?strive to train in the Bodhisattva vows.
From this I gather that practicing and holding Bodhisattva vows can bring one to Enlightenment.
"From now until samsara is emptied, I shall work for the benefit and well-being of my mothers, all sentient beings,"
Now this is something I have been pondering. Can samsara be emptied? What do you think?