In the following question, a sentence given with a blank is to be filled in with an appropriate word. Select the correct alternative out of the four.
Expectant mothers are more _________ to lung damage due to smoking.

* vulnerable: exposed to the possibility of being attacked or harmed, either physically or emotionally. It is grammatically followed by the preposition "to" in this context (vulnerable to lung damage).
disposed means inclined or willing, which does not fit the meaning.

sensitive takes "to" but usually describes a heightened sensory or allergic reaction rather than structural liability to health damage.

affected is a past participle verb form and wouldn't be followed by "more... to" in this configuration.