Q1
I started to work here last month.I am still working here now.
A. I have worked here since last month.
B.I worked here last month
->答案是A,B为何不行呢

B就单这样一句话 会让人认为你现在已经不在这里工作了(只有一题?)

B单纯表达上个月真的有在这工作，但现在有没有不知道。