1) in the C example above, can we use within instead? so This document explains our practice of limiting the time within which we will raise an original income tax assessment for a trustee.
With periods of time, "in" and "within" are usually interchangeable to mean that the period in question should not be exceeded.
2) What about for which, have I applied correctly in the sentence below.
I bought an expensive bag for which it is used for attending a VIP meeting?
No, the sentence above does not work. Perhaps you wanted to say:
- I bought an expensive bag for attending a VIP meeting.
This is an example where "for which" can be used:
- I bought an expensive bag for which I paid a fortune (I paid a fortune for the bag).
3) Can you give a good example the use of by which? this seems to be common as well.
- Please tell me the deadline by which I have to submit the documents.