Umi-tomboy
i really like the figure a and b but on figure a the higher foot seems like its been turned to much
heart From a martial artists perspective I'd say the foot is anotomically done right. When you're stepping into a side kick (yoko geri, sorry karate terminology) the foot you're balancing on really gets turned out like that if you deliver the kick with enough height, power and forward momentum.
Nit picking though... the right knee should be bent slightly to show the character is more grouned with solid balance (a kick actually hitting the target would more likely send your own character flying).
Secondly, though this might be personal preference, I'd keep the right arm up off the leg and in a more ready position so when the character steps down she's in a better position stepping down to attack or defend as necessary. And it would show a character more confident in their techniques. An arm down like that almost says, "I'm ready to fall down and catch myself now."
You're art style is very nice. Everything is well thought out. The body is anatomical and moves naturally. The wrinkles in the clothes are nicely placed to emphasise you're character's movements. Some properly placed speed lines and effects would bring the action scenes to life and make it easier to read the motion.
Keep working hard and polishing your style of art ^_^