since引导的时间状语何时用现在完成时,现在完成进行时

Sorry,for my misunderstanding and misleading advice.
I thought B says " been improving a lot." in the Perfect continous tense.But it isn't.
In this case,my judgement should be changed like this:
1.Both B & D are correct.
2.In terms of the best choice,it should be D.
Because in most cases,we don't use the passive voice when we say,sth gets better = improve.
sth + be improved,the passive voice,is also possible,when you especially emphasizes the passive action,which sound a little bit unnatural.

有since这个现在完成时的标志词自然选D，且B为被动语态，不适用

D 强调结果，英语自八月后现在已经有所提高
现在完成时和现在完成进行时区别在于：现在完成进行时强调的是动作的过程，而现在完成时强调的动作的结果和影响。
I have been writing letters the whole morning and I have written five now.
但要注意对于有些含有持续意义的动词来说，现在完成时和现在完成进行时可以互换...