When I reached London I found waiting for me an urgent request that I should go to Mrs. Strickland's as soon after dinner as I could. I found her with Colonel MacAndrew and his wife. Mrs. Strickland's sister was older than she, not unlike her, but more faded; and she had the efficient air, as though she carried the British Empire in her pocket, which the wives of senior officers acquire from the consciousness of belonging to a superior caste. Her manner was brisk, and her good-breeding scarcely concealed her conviction that if you were not a soldier you might as well be a counter-jumper. She hated the Guards, whom she thought conceited, and she could not trust herself to speak of their ladies, who were so remiss in calling. Her gown was dowdy and expensive.

请教老师：上面节选，整体使用了一般过去时，但为什么在which the wives of senior officers acquire from the consciousness of belonging to a superior caste.中，谓语动词acquire使用了一般现在时呢？这句属于非限制性定语从句，其中acquire的宾语应该是and she had the efficient air 中的the efficient air吧？