a week ago 一周前,用于一般过去时. since last week自从上周以来,用于现在完成时 He came here a week ago . He has been here since last week . 再问: 有个问题是甘的 我不是很明点解选b hao long did you get ill? ----------------- a a week b a week ago c since last week 应该意思上c才对的 再答: 问句是一般过去时,回答也应该用一般过去时,故B对。