3. Supongamos que un hombre no calvo (cc) se casa una mujer no calva (Cc) heterocigótica; entonces de las hijas e hijos varones que ellos tengan, es correcto afirmar que * B. la mitad de los varones será calva y todas las hijas no serán calvas.
porque es correcto

Yes it’s grammatically correct, but the phrase possibly doesn’t have quite the meaning you think it does.

To my mind, ‘I am balding’ is a description of my conditions/state right now. If I have already lost a large percentage of my hair, then I might describe myself as ‘I am a balding, 60 year old father of two’.

However, if you wanted to know whether I still have a full head of hair, my response is more likely to be ‘No, I’m going bald’ or ‘No, I’ve started to go bald’.

‘No, I am balding’ just doesn’t sound quite right (in UK English), although there’s nothing grammatically wrong with it.

trachea, alveoli, lung capillaries, arteries