单选题 ______ Mr. Hall admits that he pushed too hard, and ultimately his efforts failed.
【正确答案】 D
【答案解析】[解析] A项“in essence”意为“本质上；大体上；其实”；B项“in due course”意为“在今后适当的时候”；C项“on average”意为“平均来说”；D项“in retrospect”意为“回想起来，回顾往事”。本句是说霍尔先生现在回想起来，因此选择D。