It wasn't ten seconds ___(later/ before)when sth happaned.

问题描述:

It wasn't ten seconds ___(later/ before)when sth happaned.
为什么用later?请详细分析,
It wasn't ten seconds ___ when a student shouted:'Tom is talking again!

翻译:直到10秒后才有一个学生大喊:“Tom 又在讲话了!”
如果填入before首先翻译不通顺,其次从句子结构上来说,大喊应该是发生在10秒钟以后的,注意句子中的wasn't是否定结构.
希望能帮上您.