Tom has been watching TV ______ he came home 是“when?”还是“since?”

问题描述:

Tom has been watching TV ______ he came home 是“when?”还是“since?”

has been watching强调过去一直做某事 直到现在 有可能还会继续
题目应该这样翻译 自从tom回家开始 他一直在看电视
所以应该用since