Fill in the blank with a suitable preposition.
She was anxious _______ her mom's health.
The preposition ‘about’ is used with 'anxious' to mean being worried about someone or something. In the given sentence the person is worried about her mom’s health, hence option B is correct. Whereas the phrasal verb ‘anxious to’ is used to denote being excited or nervous about doing something. Thus ‘anxious to’ needs to be followed by an action. Since ‘her mom’s health’ is not related to doing an action option A is incorrect. On the other hand ‘by’ and ‘at’ are unsuitable in the given sentence because ‘by’ is used to denote an agent or a means, while ‘at’ is used to denote a unit of time or an exact place/position. Since the words that follow the blanks are neither of these options C and D are incorrect.