你以前每隔多久打一次电话回家？
How often did you use to call home when you were studying abroad?
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did英 /dɪd/|美 /dɪd/
use英 /juːz/|美 /juz/|英 /juːs/|美 /jus/
to英 /tuː/|美 /tu/|英 /tə/|美 /tə/
解释
how often特殊疑问句：how often询问过去习惯的频率，did后接use to原形构成疑问。
How often did you use to call home when you were studying abroad?
how often特殊疑问句：how often询问过去习惯的频率，did后接use to原形构成疑问。