题干
你昨天不可能碰到汤姆，他已经动身前往美国了。（could have done）
答案(点此获取答案解析）
You couldn't have met Tom yesterday, because/as/for/since he already had set off for /set out for/left for/gone to America.
You couldn't have met Tom yesterday. He already had set off for/set out for/left for/gone to America.
