since+一段时间+ago,前面主语难道必须要用现在完成时态吗并举出例子

Question

since +一段时间+ ago,前面主语难道必须要用现在完成时态吗
并举出例子

Answer 1

for和since是现在完成时的提示词汇,但两者用法不同：
(1)for和表示一段时间的词组连用,如：
for three minutes,for six hours,for nine days
for twelve weeks,for fifteen months,for thirty years
(2)since和表示过去某一时刻的词或词组连用,如：
since nine o'clock this morning,since three weeks ago
since last Friday,since September