一九六六年秋天，在西安工作的大哥回家探亲时，有空他便给我辅导一些数学知识。
B-Time I-Time I-Time I-Time I-Time I-Time I-Time O O B-Location I-Location O O O B-Person I-Person B-Location I-Location B-Time I-Time I-Time O O O B-Person O O B-Person O O B-Metric I-Metric B-Thing I-Thing I-Thing I-Thing O