单选题 The time will come ______ man can fly to outer space at his leisure.

【正确答案】 A
【答案解析】同位语从句。that引导的同位语从句解释说明了主句。易混淆选项是when,如果用when引导,就成了定语从句,应紧跟先行词time,因此when不是正确答案。