These days 用什么时态,和those days有什么区别

亲：
these days 可以用现在进行时,表示当前这段时间正在进行,也可以用现在完成时,表示现在已经完成时.
I am writing a book these days.
I have written a book these days.
those days用于一般过去时或者过去进行时,表示当时正在进行.
I wrote a book those days.
I was writing a book those days.