作业帮It is 3 years_____he joined the army.
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It is 3 years_____he joined the army.
It is 3 years_____he joined the army.
It is 3 years_____he joined the army.
since
意思是他参军已经三年了
原句就有语法错误,如果要用before,前面就应是was.如果要用since,前面就应是has been.所以我认为题目出错了.