题目

John went to see his doctor one day, because he had a stomach ache for a long time. After checking John carefully, the doctor said, “Well, there’s nothing wrong with you, I’m pleased to say. Your only trouble is that you worry too much. Do you know, I had a man with the same trouble as you here a few weeks ago, and I gave him the same advice as I am going to give you. He was worried because he couldn’t pay his tailor’s（裁缝的） bills. I told him not to worry about the bills any more. He took my advice and when he came to see me again two days ago, he told me that he now felt quMrs. White became a teacher in 1985. She ________ for twenty years by next summer. [　　] A．will teachB．would have taught C．has been teachingD．will have been teaching