Today I have a grammar question for you. Please try to guess/explain why ‘a’ article in the highlighted part of the sentence!
Mrs. Gardiner's caution to Elizabeth was punctually and kindly given on the first favourable opportunity of speaking to her alone; after honestly telling her what she thought, she thus went on:
"You are too sensible a girl, Lizzy, to fall in love merely because you are warned against it; and, therefore, I am not afraid of speaking openly. Seriously, I would have you be on your guard. Do not involve yourself or endeavour to involve him in an affection which the want of fortune would make so very imprudent. I have nothing to say against him; he is a most interesting young man; and if he had the fortune he ought to have, I should think you could not do better. But as it is, you must not let your fancy run away with you. You have sense, and we all expect you to use it. Your father would depend on your resolution and good conduct, I am sure. You must not disappoint your father."