A partial letter:

' Hello Grammar Teacher,

I would like to thank you for your edition.However, I cannot understand/ have not understood/have not been understanding the logic of your edition.Could you ...'

Hello Grammar Teacher/Teachers,

1. At the time of writing the letter, I still have not understood the logic of the edition.What is the correct tense or tenses such as a present or past tense I should or can use in the underlined words in order to communicate with my Grammar Teacher ?

2. Could you tell me whether the following words can be used in order to replace the words in the underlined words of the letter or not ?

a. have yet to understand

b. am not able to understand

c. could not understand

Thank you.

With best wishes.

Hello Grammar Teacher,

I would like to thank you for your advice. I have accepted item b.,that is, am not able to understand.However, I am doubtful about the rest.

Could you tell me whether those underlined words,including item a.(have yet to understand ) can be accepted as alternatives in that situation ?

Further, I would like to thank you for recommending the article on TENSES. I have read them and they are easy to comprehend but they do not

show us when  to use them.

Thank you.

With best wishes.

In any written communication, clarity is very important. Items a and c are not suitable.

Item a (have yet to understand) means or implies that you will understand in due course even without aid, while item c (could not understand) is a past situation without indicating the present state and may imply that you can understand now.

The article on TENSES is actually a blog post which may not be suitable for elaborating their uses.

You may see useful links in another member's reply.