第23题: [单项选择]Since you have failed three of the last four tests, you cannot afford to be ______ about passing for the term. A. courteous B. relevant C. optimistic D. passive 参考答案:C 答案解析:(optimistic乐观的)。句意为:你在以往的四次考试中有三次不及格,因此不能对通过学期考试感到乐观。A.courteous有礼貌的;B.relevant相关的;D.passive被动的。