围绕本课标题 A perfect alibi 极好的不在犯罪现场的罪证（侦探对话）主题，AI 老师会出 若干个简单问题，
每个问题听完后，用 完整句子口头作答。
⚠️ 尽量说完整句子，不要只说一个词；优先用本课句型与词语：At the time the murder was committed / travelling on the 8 o'clock train to London / Do you always catch such an early train / I must be at work at 10 o'clock / My employer will confirm / I was there on time / Would a later train get you to work on time / I never catch a later train / At what time did you arrive at the station / bought a paper and waited for the train / notice anything unusual / Of course not / you are not telling the truth / you caught the 8.25 / would still get you to work on time / the 8 o'clock train did not run at all / It broke down at Ferngreen station / was taken off the line